\input texinfo @c -*-texinfo-*- @c %**start of header @setfilename autoconf.info @settitle Autoconf @finalout @setchapternewpage odd @setcontentsaftertitlepage @include version.texi @c A simple macro for optional variables. @macro ovar{varname} @r{[}@var{\varname\}@r{]} @end macro @c I don't like the way URL are displayed in TeX with @uref. @ifhtml @macro href{url, title} @uref{\url\, \title\} @end macro @end ifhtml @ifnothtml @macro href{url, title} \title\@footnote{\title\, @url{\url\}.} @end macro @end ifnothtml @dircategory GNU admin @direntry * Autoconf: (autoconf). Create source code configuration scripts @end direntry @dircategory Individual utilities @direntry * autoscan: (autoconf)autoscan Invocation. Semi-automatic @file{configure.in} writing * ifnames: (autoconf)ifnames Invocation. Listing the conditionals in source code * autoconf: (autoconf)autoconf Invocation. How to create configuration scripts * autoreconf: (autoconf)autoreconf Invocation. Remaking multiple @code{configure} scripts * configure: (autoconf)configure Invocation. Configuring a package * config.status: (autoconf)config.status Invocation. Recreating a configuration @end direntry @ifinfo Autoconf: Creating Automatic Configuration Scripts, by David MacKenzie. This file documents the GNU Autoconf package for creating scripts to configure source code packages using templates and an @code{m4} macro package. Copyright (C) 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. @ignore Permission is granted to process this file through TeX and print the results, provided the printed document carries copying permission notice identical to this one except for the removal of this paragraph (this paragraph not being relevant to the printed manual). @end ignore Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. @end ifinfo @titlepage @title Autoconf @subtitle Creating Automatic Configuration Scripts @subtitle Edition @value{EDITION}, for Autoconf version @value{VERSION} @subtitle @value{UPDATED} @author David MacKenzie and Ben Elliston @c I think I've rewritten all of Noah and Roland's contributions by now. @page @vskip 0pt plus 1filll Copyright @copyright{} 1992, 93, 94, 95, 96, 98, 99, 2000 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. @end titlepage @c Define an environment variable index. @defcodeindex ev @c Define an output variable index. @defcodeindex ov @c Define a CPP variable index. @defcodeindex cv @c Define a macro index that @@defmac doesn't write to. @defcodeindex ma @node Top, Introduction, (dir), (dir) @comment node-name, next, previous, up @ifinfo This file documents the GNU Autoconf package for creating scripts to configure source code packages using templates and the GNU M4 macro package. This is edition @value{EDITION}, for Autoconf version @value{VERSION}. @end ifinfo @c The master menu, created with texinfo-master-menu, goes here. @menu * Introduction:: Autoconf's purpose, strengths, and weaknesses * The GNU build system:: * Making configure Scripts:: How to organize and produce Autoconf scripts * Setup:: Initialization and output * Existing Tests:: Macros that check for particular features * Writing Tests:: How to write new feature checks * Results:: What to do with results from feature checks * Writing Macros:: Adding new macros to Autoconf * Manual Configuration:: Selecting features that can't be guessed * Site Configuration:: Local defaults for @code{configure} * Running configure scripts:: How to use the Autoconf output * config.status Invocation:: Recreating a configuration * Obsolete Constructs:: Kept for backward compatibility * Questions:: Questions about Autoconf, with answers * History:: History of Autoconf * Environment Variable Index:: Index of environment variables used * Output Variable Index:: Index of variables set in output files * Preprocessor Symbol Index:: Index of C preprocessor symbols defined * Macro Index:: Index of Autoconf macros * Concept Index:: General index @detailmenu --- The Detailed Node Listing --- Making @code{configure} Scripts * Writing configure.in:: What to put in an Autoconf input file * autoscan Invocation:: Semi-automatic @file{configure.in} writing * ifnames Invocation:: Listing the conditionals in source code * autoconf Invocation:: How to create configuration scripts * autoreconf Invocation:: Remaking multiple @code{configure} scripts Writing @file{configure.in} * Shell Script Compiler:: Autoconf as solution of a problem * Autoconf Language:: Programming in Autoconf * configure.in Layout:: Standard organization of configure.in Initialization and Output Files * Notices:: Copyright, version numbers in @code{configure} * Input:: Where Autoconf should find files * Output:: Outputting results from the configuration * Configuration Actions:: Preparing the output based on results * Configuration Files:: Creating output files * Makefile Substitutions:: Using output variables in @file{Makefile}s * Configuration Headers:: Creating a configuration header file * Configuration Commands:: Running arbitrary instantiation commands * Configuration Links:: Links depending from the configuration * Subdirectories:: Configuring independent packages together * Default Prefix:: Changing the default installation prefix Substitutions in Makefiles * Preset Output Variables:: Output variables that are always set * Installation Directory Variables:: Other preset output variables * Build Directories:: Supporting multiple concurrent compiles * Automatic Remaking:: Makefile rules for configuring Configuration Header Files * Header Templates:: Input for the configuration headers * autoheader Invocation:: How to create configuration templates * Autoheader Macros:: How to specify CPP templates Existing Tests * Common Behavior:: Macros' standard schemes * Alternative Programs:: Selecting between alternative programs * Libraries:: Library archives that might be missing * Library Functions:: C library functions that might be missing * Header Files:: Header files that might be missing * Declarations:: Declarations that may be missing * Structures:: Structures or members that might be missing * Types:: Types that might be missing * Compilers and Preprocessors:: Checking for compiling programs * C Compiler Characteristics:: * Fortran 77 Compiler Characteristics:: * System Services:: Operating system services * UNIX Variants:: Special kludges for specific UNIX variants Common Behavior * Standard Symbols:: Symbols defined by the macros * Default Includes:: Includes used by the generic macros Alternative Programs * Particular Programs:: Special handling to find certain programs * Generic Programs:: How to find other programs Library Functions * Particular Functions:: Special handling to find certain functions * Generic Functions:: How to find other functions Header Files * Particular Headers:: Special handling to find certain headers * Generic Headers:: How to find other headers Declarations * Particular Declarations:: Macros to check for certain declarations * Generic Declarations:: How to find other declarations Structures * Particular Structures:: Macros to check for certain structure members * Generic Structures:: How to find other structure members Types * Particular Types:: Special handling to find certain types * Generic Types:: How to find other types Writing Tests * Examining Declarations:: Detecting header files and declarations * Examining Syntax:: Detecting language syntax features * Examining Libraries:: Detecting functions and global variables * Run Time:: Testing for run-time features * Portable Shell:: Shell script portability pitfalls * Multiple Cases:: Tests for several possible values * Language Choice:: Selecting which language to use for testing Checking Run Time Behavior * Test Programs:: Running test programs * Guidelines:: General rules for writing test programs * Test Functions:: Avoiding pitfalls in test programs Portable Shell Programming * Shellology:: A zoology of shells * Special Shell Variables:: Variables you should not change * Shell Substitutions:: Test and assign * Limitations of Builtins:: Portable use of not so portable /bin/sh * Limitations of Usual Tools:: Portable use of portable tools Results of Tests * Defining Symbols:: Defining C preprocessor symbols * Setting Output Variables:: Replacing variables in output files * Caching Results:: Speeding up subsequent @code{configure} runs * Printing Messages:: Notifying @code{configure} users Caching Results * Cache Variable Names:: Shell variables used in caches * Cache Files:: Files @code{configure} uses for caching Writing Macros * Macro Definitions:: Basic format of an Autoconf macro * Macro Names:: What to call your new macros * Quoting:: Protecting macros from unwanted expansion * Reporting Messages:: Notifying @code{autoconf} users * Dependencies Between Macros:: What to do when macros depend on other macros * Obsoleting Macros:: Warning about old ways of doing things * Coding Style:: Writing Autoconf macros @`a la Autoconf Quoting * Active Characters:: Characters that change the behavior of m4 * One Macro Call:: Quotation and one macro call * Quotation and Nested Macros:: Macros calling macros * Quotation Rule Of Thumb:: One parenthesis, one quote Dependencies Between Macros * Prerequisite Macros:: Ensuring required information * Suggested Ordering:: Warning about possible ordering problems Manual Configuration * Specifying Names:: Specifying the system type * Canonicalizing:: Getting the canonical system type * Using System Type:: What to do with the system type Site Configuration * External Software:: Working with other optional software * Package Options:: Selecting optional features * Pretty Help Strings:: Formating help string * Site Details:: Configuring site details * Transforming Names:: Changing program names when installing * Site Defaults:: Giving @code{configure} local defaults Transforming Program Names When Installing * Transformation Options:: @code{configure} options to transform names * Transformation Examples:: Sample uses of transforming names * Transformation Rules:: @file{Makefile} uses of transforming names Running @code{configure} Scripts * Basic Installation:: Instructions for typical cases * Compilers and Options:: Selecting compilers and optimization * Multiple Architectures:: Compiling for multiple architectures at once * Installation Names:: Installing in different directories * Optional Features:: Selecting optional features * System Type:: Specifying the system type * Sharing Defaults:: Setting site-wide defaults for @code{configure} * Environment Variables:: Defining environment variables. * configure Invocation:: Changing how @code{configure} runs Obsolete Constructs * Obsolete config.status Use:: Different calling convention * acconfig.h:: Additional entries in @file{config.h.in} * autoupdate Invocation:: Automatic update of @file{configure.in} * Obsolete Macros:: Backward compatibility macros * Autoconf 1:: Tips for upgrading your files Upgrading From Version 1 * Changed File Names:: Files you might rename * Changed Makefiles:: New things to put in @file{Makefile.in} * Changed Macros:: Macro calls you might replace * Changed Results:: Changes in how to check test results * Changed Macro Writing:: Better ways to write your own macros Questions About Autoconf * Distributing:: Distributing @code{configure} scripts * Why GNU m4:: Why not use the standard M4? * Bootstrapping:: Autoconf and GNU M4 require each other? * Why Not Imake:: Why GNU uses @code{configure} instead of Imake History of Autoconf * Genesis:: Prehistory and naming of @code{configure} * Exodus:: The plagues of M4 and Perl * Leviticus:: The priestly code of portability arrives * Numbers:: Growth and contributors * Deuteronomy:: Approaching the promises of easy configuration @end detailmenu @end menu @c ============================================================= Introduction. @node Introduction, The GNU build system, Top, Top @chapter Introduction @flushright A physicist, an engineer, and a computer scientist were discussing the nature of God. Surely a Physicist, said the physicist, because early in the Creation, God made Light; and you know, Maxwell's equations, the dual nature of electro-magnetic waves, the relativist consequences@dots{} An Engineer!, said the engineer, because before making Light, God split the Chaos into Land and Water; it takes a hell of an engineer to handle that big amount of mud, and orderly separation of solids from liquids@dots{} The computer scientist shouted: And the Chaos, where do you think it was coming from, hmm? ---Anonymous @end flushright @c (via Franc,ois Pinard) Autoconf is a tool for producing shell scripts that automatically configure software source code packages to adapt to many kinds of @sc{unix}-like systems. The configuration scripts produced by Autoconf are independent of Autoconf when they are run, so their users do not need to have Autoconf. The configuration scripts produced by Autoconf require no manual user intervention when run; they do not normally even need an argument specifying the system type. Instead, they individually test for the presence of each feature that the software package they are for might need. (Before each check, they print a one-line message stating what they are checking for, so the user doesn't get too bored while waiting for the script to finish.) As a result, they deal well with systems that are hybrids or customized from the more common @sc{unix} variants. There is no need to maintain files that list the features supported by each release of each variant of @sc{unix}. For each software package that Autoconf is used with, it creates a configuration script from a template file that lists the system features that the package needs or can use. After the shell code to recognize and respond to a system feature has been written, Autoconf allows it to be shared by many software packages that can use (or need) that feature. If it later turns out that the shell code needs adjustment for some reason, it needs to be changed in only one place; all of the configuration scripts can be regenerated automatically to take advantage of the updated code. The Metaconfig package is similar in purpose to Autoconf, but the scripts it produces require manual user intervention, which is quite inconvenient when configuring large source trees. Unlike Metaconfig scripts, Autoconf scripts can support cross-compiling, if some care is taken in writing them. @c FIXME: Tom, your cue is here. There are several jobs related to making portable software packages that Autoconf currently does not do. Among these are automatically creating @file{Makefile} files with all of the standard targets, and supplying replacements for standard library functions and header files on systems that lack them. Work is in progress to add those features in the future. Autoconf imposes some restrictions on the names of macros used with @code{#if} in C programs (@pxref{Preprocessor Symbol Index}). Autoconf requires @sc{gnu} M4 in order to generate the scripts. It uses features that some @sc{unix} versions of M4, including @sc{gnu} M4 1.3, do not have. You must use version 1.4 or later of @sc{gnu} M4. @xref{Autoconf 1}, for information about upgrading from version 1. @xref{History}, for the story of Autoconf's development. @xref{Questions}, for answers to some common questions about Autoconf. See the @href{http://www.gnu.org/software/autoconf/autoconf.html, Autoconf web page} for up to date information, details on the mailing lists, pointers to a list of known bugs, etc. Mail suggestions to @email{autoconf@@gnu.org, the Autoconf mailing list}. Bug reports should be preferably submitted to the @href{http://sources.redhat.com/cgi-bin/gnatsweb.pl?database=autoconf, Autoconf Gnats database}, or sent to @email{bug-autoconf@@gnu.org, the Autoconf Bugs mailing list}. If possible, first check that your bug is not already solved in current development versions, and that it has not been reported yet. Be sure to include all the needed information and a short @file{configure.in} that demonstrates the problem. Autoconf's development tree is accessible via @sc{cvs}, see the Autoconf web page for details. There is also a @href{http://subversions.gnu.org/cgi-bin/cvsweb/autoconf/, @sc{cvs}web interface to the Autoconf development tree}. Patches relative to the current @sc{cvs} version can be sent for review to the @email{autoconf-patches@@gnu.org, Autoconf Patches mailing list}. Because of its mission, Autoconf includes only a set of highly used macros that have already demonstrated their usefulness. Nevertheless, if you wish to share your macros, or find existing ones, see the @href{http://research.cys.de/autoconf-archive/, Autoconf Macro Repository}, which is kindly run by @email{simons@@research.cys.de, Peter Simons}. @c ================================================= The GNU build system @node The GNU build system, Making configure Scripts, Introduction, Top @chapter The GNU build system @emph{This chapter is still under work. It will be ready for the release, but most probably not for the next betas.} I'm unsure about the title. Move the dissertation `A shell script compiler' here. The text above, probably starting at `There are several jobs...', should be moved here. Hm? Talk about Automake, Libtool. Explain the concept of system.h. Promote Bison, Flex and other GNU tools. Provide pointers to the various documentations and tutorials (books, web etc.). Explain that learning is painful, agreed, but getting inspiration is the way out. Fetish, libit, liberty. @c ================================================= Making configure Scripts. @node Making configure Scripts, Setup, The GNU build system, Top @chapter Making @code{configure} Scripts @cindex @file{aclocal.m4} @cindex @code{configure} The configuration scripts that Autoconf produces are by convention called @code{configure}. When run, @code{configure} creates several files, replacing configuration parameters in them with appropriate values. The files that @code{configure} creates are: @itemize @bullet @item one or more @file{Makefile} files, one in each subdirectory of the package (@pxref{Makefile Substitutions}); @item optionally, a C header file, the name of which is configurable, containing @code{#define} directives (@pxref{Configuration Headers}); @item a shell script called @file{config.status} that, when run, will recreate the files listed above (@pxref{config.status Invocation}); @item an optional shell script normally called @file{config.cache} (created when using @samp{configure --cache-file=config.cache}) that saves the results of running many of the tests (@pxref{Cache Files}); @item a file called @file{config.log} containing any messages produced by compilers, to help debugging if @code{configure} makes a mistake. @end itemize To create a @code{configure} script with Autoconf, you need to write an Autoconf input file @file{configure.in} and run @code{autoconf} on it. If you write your own feature tests to supplement those that come with Autoconf, you might also write files called @file{aclocal.m4} and @file{acsite.m4}. If you use a C header file to contain @code{#define} directives, you might also run @code{autoheader}, and you will distribute the generated file @file{config.h.in} with the package. Here is a diagram showing how the files that can be used in configuration are produced. Programs that are executed are suffixed by @samp{*}. Optional files are enclosed in square brackets (@samp{[]}). @code{autoconf} and @code{autoheader} also read the installed Autoconf macro files (by reading @file{autoconf.m4}). @noindent Files used in preparing a software package for distribution: @example @group your source files --> [autoscan*] --> [configure.scan] --> configure.in configure.in --. .------> autoconf* -----> configure +---+ [aclocal.m4] --+ `---. [acsite.m4] ---' | +--> [autoheader*] -> [config.h.in] [acconfig.h] ----. | +-----' [config.h.top] --+ [config.h.bot] --' Makefile.in -------------------------------> Makefile.in @end group @end example @noindent Files used in configuring a software package: @example @group .-------------> [config.cache] configure* ------------+-------------> config.log | [config.h.in] -. v .-> [config.h] -. +--> config.status* -+ +--> make* Makefile.in ---' `-> Makefile ---' @end group @end example @menu * Writing configure.in:: What to put in an Autoconf input file * autoscan Invocation:: Semi-automatic @file{configure.in} writing * ifnames Invocation:: Listing the conditionals in source code * autoconf Invocation:: How to create configuration scripts * autoreconf Invocation:: Remaking multiple @code{configure} scripts @end menu @node Writing configure.in, autoscan Invocation, Making configure Scripts, Making configure Scripts @section Writing @file{configure.in} To produce a @code{configure} script for a software package, create a file called @file{configure.in} that contains invocations of the Autoconf macros that test the system features your package needs or can use. Autoconf macros already exist to check for many features; see @ref{Existing Tests}, for their descriptions. For most other features, you can use Autoconf template macros to produce custom checks; see @ref{Writing Tests}, for information about them. For especially tricky or specialized features, @file{configure.in} might need to contain some hand-crafted shell commands. The @code{autoscan} program can give you a good start in writing @file{configure.in} (@pxref{autoscan Invocation}, for more information). @menu * Shell Script Compiler:: Autoconf as solution of a problem * Autoconf Language:: Programming in Autoconf * configure.in Layout:: Standard organization of configure.in @end menu @node Shell Script Compiler, Autoconf Language, Writing configure.in, Writing configure.in @subsection A Shell Script Compiler Like for any other language, to properly program in Autoconf, i.e., the language in which you write @file{configure.in}, you must understand @emph{what} is the problem it tries to answer, and @emph{how} it does. The problem Autoconf addresses is that the world is a mess: after all, you are using Autoconf in order to have your package compile easily on all sort of different systems, some of them being extremely hostile. But Autoconf itself suffers from these differences: @code{configure} must run on all those systems, hence @code{configure} must use the least common divisor between all supported system. Naturally, you orient yourself towards shell scripts. And in fact, there is not even the need for a tool like @code{autoconf}: a set of properly written shell functions is way enough to make it easy to write @code{configure} scripts by hand. Sigh! Unfortunately, shell functions do not belong to the least common divisor, therefore, where you'd define a function and use it ten times, you need to write ten times its body. Therefore, what is really needed is some kind of compiler, @code{autoconf}, which takes an Autoconf program, @file{configure.in}, and transform it in a portable shell script, @code{configure}. How does @code{autoconf} perform this task? Two obvious solutions: creating a brand new language, or extending an existing one. The former option is very attractive: all sort of optimizations could easily be implemented in the compiler, many rigorous checks could be performed on the Autoconf program, and in particular, it would be extremely easy to reject any non portable construct etc. Alternatively, you can extend an existing language, of course, the @code{sh} language. Autoconf does the latter: it is an layer on top of @code{sh}. Quite naturally then, it has been chosen to implement @code{autoconf} as a macro expander, i.e., a program that takes a text in input and repeatedly performs @dfn{macro expansions}, repeatedly replaces macro uses with macro bodies. Instead of implementing a dedicated Autoconf macro expander, it is natural to use an existing general purpose macro expander, such as M4, and implement the extensions as a set of M4 macros. @node Autoconf Language, configure.in Layout, Shell Script Compiler, Writing configure.in @subsection The Autoconf Language @cindex quotation The Autoconf language is very different from usual languages because you handle actual code just as plain text. Where in C for instance, data and instructions have very different syntactic status, in Autoconf their status is rigorously the same. Therefore we need a means to distinguish literal strings from text to be expanded: quotation. When calling macros that take arguments, there must not be any blank space between the macro name and the open parenthesis. Arguments should be enclosed within the M4 quote characters @samp{[} and @samp{]}, and are separated by a comma. Any leading spaces in arguments are ignored, unless they are quoted. You may safely leave out the quotes when the argument is simple text, but @emph{always} quote complex arguments such as other macro calls. This rule recursively applies for each macro call, including macro called from other macros. For instance: @example AC_CHECK_HEADER([stdio.h], [AC_DEFINE([HAVE_STDIO_H])], [AC_MSG_ERROR([Sorry, can't do anything for you])]) @end example @noindent is perfectly quoted. You may safely simplify quotation to @example AC_CHECK_HEADER(stdio.h, [AC_DEFINE(HAVE_STDIO_H)], [AC_MSG_ERROR([Sorry, can't do anything for you])]) @end example @noindent Notice that the argument of @code{AC_MSG_ERROR} is still quoted, otherwise its comma would have been understood as an argument separator. The following example is wrong and dangerous, as it is underquoted: @example AC_CHECK_HEADER(stdio.h, AC_DEFINE(HAVE_STDIO_H), AC_MSG_ERROR([Sorry, can't do anything for you])) @end example You may have to use text that also resembles a macro call. In this case, you must quote this text at top level: @example echo "Hard rock was here! --[AC_DC]" @end example @noindent which will result in @example echo "Hard rock was here! --AC_DC" @end example @noindent in @code{configure}. Since there is an additional quoting level for each macro invocation, this results in @emph{double quoting all the literal strings}: @example AC_MSG_WARN([[AC_DC stinks --Iron Maiden]]) @end example You are now able to understand one of the constructs of Autoconf that has continuously been misunderstood... The rule of thumb is that @emph{whenever you expect macro expansion, expect quote expansion}, i.e., expect one level of quotes to be lost. For instance @example AC_COMPILE_IFELSE([char b[10];],, (exit 1); exit) @end example @noindent is incorrect: here the first argument of @code{AC_COMPILE_IFELSE}, is @samp{char b[10];}, and it will be expanded once, which results in @samp{char b10;}. There was a idiom developed in the Autoconf world to address this issue, based on the M4 @code{changequote} primitive, but do not use it! Let's take a closer look: the author meant the first argument to be understood as a literal, and therefore it must be quoted twice: @example AC_COMPILE_IFELSE([[char b[10];]],, (exit 1); exit) @end example @noindent and voil@`a! You really produced @samp{char b[10];}. The careful reader will note that the so-called perfectly quoted @code{AC_CHECK_HEADER} example above is actually lacking three pairs of quotes! Nevertheless, for sake of readability, double quotation of literals is used only where needed. Some macros take optional arguments, which this documentation represents @ovar{arg} (not to be confounded with the quote characters). You may just leave them empty, or use @samp{[]} to make explicit the emptiness of the argument. Finally you may simply leave out the trailing commas. The three lines below are equivalent: @example AC_CHECK_HEADERS(stdio.h, [], []) AC_CHECK_HEADERS(stdio.h,,) AC_CHECK_HEADERS(stdio.h) @end example It is best to put each macro call on its own line in @file{configure.in}. Most of the macros don't add extra newlines; they rely on the newline after the macro call to terminate the commands. This approach makes the generated @code{configure} script a little easier to read by not inserting lots of blank lines. It is generally safe to set shell variables on the same line as a macro call, because the shell allows assignments without intervening newlines. You can include comments in @file{configure.in} files by starting them with the @samp{#}. For example, it is helpful to begin @file{configure.in} files with a line like this: @example # Process this file with autoconf to produce a configure script. @end example @node configure.in Layout, , Autoconf Language, Writing configure.in @subsection Standard @file{configure.in} Layout The order in which @file{configure.in} calls the Autoconf macros is not important, with a few exceptions. Every @file{configure.in} must contain a call to @code{AC_INIT} before the checks, and a call to @code{AC_OUTPUT} at the end (@pxref{Output}). Additionally, some macros rely on other macros having been called first, because they check previously set values of some variables to decide what to do. These macros are noted in the individual descriptions (@pxref{Existing Tests}), and they also warn you when creating @code{configure} if they are called out of order. To encourage consistency, here is a suggested order for calling the Autoconf macros. Generally speaking, the things near the end of this list could depend on things earlier in it. For example, library functions could be affected by types and libraries. @display @group Autoconf requirements @code{AC_INIT(@var{package}, @var{version}, @var{bug-report-address})} information on the package checks for programs checks for libraries checks for header files checks for types checks for structures checks for compiler characteristics checks for library functions checks for system services @code{AC_CONFIG_FILES(@r{[}@var{file@dots{}}@r{]})} @code{AC_OUTPUT} @end group @end display @node autoscan Invocation, ifnames Invocation, Writing configure.in, Making configure Scripts @section Using @code{autoscan} to Create @file{configure.in} @cindex @code{autoscan} The @code{autoscan} program can help you create a @file{configure.in} file for a software package. @code{autoscan} examines source files in the directory tree rooted at a directory given as a command line argument, or the current directory if none is given. It searches the source files for common portability problems and creates a file @file{configure.scan} which is a preliminary @file{configure.in} for that package. You should manually examine @file{configure.scan} before renaming it to @file{configure.in}; it will probably need some adjustments. Occasionally @code{autoscan} outputs a macro in the wrong order relative to another macro, so that @code{autoconf} produces a warning; you need to move such macros manually. Also, if you want the package to use a configuration header file, you must add a call to @code{AC_CONFIG_HEADERS} (@pxref{Configuration Headers}). You might also have to change or add some @code{#if} directives to your program in order to make it work with Autoconf (@pxref{ifnames Invocation}, for information about a program that can help with that job). @code{autoscan} uses several data files, which are installed along with the distributed Autoconf macro files, to determine which macros to output when it finds particular symbols in a package's source files. These files all have the same format. Each line consists of a symbol, whitespace, and the Autoconf macro to output if that symbol is encountered. Lines starting with @samp{#} are comments. @code{autoscan} is only installed if you already have Perl installed. @code{autoscan} accepts the following options: @table @option @item --help @itemx -h Print a summary of the command line options and exit. @item --version @itemx -V Print the version number of Autoconf and exit. @item --verbose @itemx -v Print the names of the files it examines and the potentially interesting symbols it finds in them. This output can be voluminous. @item --autoconf-dir=@var{dir} @itemx -A @evindex AC_MACRODIR Overwrite the location where Autoconf files were installed. You can also set the @code{AC_MACRODIR} environment variable to a directory; this option overrides the environment variable. This option is rarely needed and dangerous: only when you play with different versions of Autoconf. @end table @node ifnames Invocation, autoconf Invocation, autoscan Invocation, Making configure Scripts @section Using @code{ifnames} to List Conditionals @cindex @code{ifnames} @code{ifnames} can help when writing a @file{configure.in} for a software package. It prints the identifiers that the package already uses in C preprocessor conditionals. If a package has already been set up to have some portability, this program can help you figure out what its @code{configure} needs to check for. It may help fill in some gaps in a @file{configure.in} generated by @code{autoscan} (@pxref{autoscan Invocation}). @code{ifnames} scans all of the C source files named on the command line (or the standard input, if none are given) and writes to the standard output a sorted list of all the identifiers that appear in those files in @code{#if}, @code{#elif}, @code{#ifdef}, or @code{#ifndef} directives. It prints each identifier on a line, followed by a space-separated list of the files in which that identifier occurs. @noindent @code{ifnames} accepts the following options: @table @option @item --help @itemx -h Print a summary of the command line options and exit. @item --version @itemx -V Print the version number of Autoconf and exit. @end table @node autoconf Invocation, autoreconf Invocation, ifnames Invocation, Making configure Scripts @section Using @code{autoconf} to Create @code{configure} @cindex @code{autoconf} To create @code{configure} from @file{configure.in}, run the @code{autoconf} program with no arguments. @code{autoconf} processes @file{configure.in} with the @code{m4} macro processor, using the Autoconf macros. If you give @code{autoconf} an argument, it reads that file instead of @file{configure.in} and writes the configuration script to the standard output instead of to @code{configure}. If you give @code{autoconf} the argument @option{-}, it reads the standard input instead of @file{configure.in} and writes the configuration script on the standard output. The Autoconf macros are defined in several files. Some of the files are distributed with Autoconf; @code{autoconf} reads them first. Then it looks for the optional file @file{acsite.m4} in the directory that contains the distributed Autoconf macro files, and for the optional file @file{aclocal.m4} in the current directory. Those files can contain your site's or the package's own Autoconf macro definitions (@pxref{Writing Macros}, for more information). If a macro is defined in more than one of the files that @code{autoconf} reads, the last definition it reads overrides the earlier ones. @code{autoconf} accepts the following options: @table @option @item --help @itemx -h Print a summary of the command line options and exit. @item --version @itemx -V Print the version number of Autoconf and exit. @item --verbose @itemx -v Report processing steps. @item --debug @itemx -d Don't remove the temporary files. @item --autoconf-dir=@var{dir} @itemx -A @evindex AC_MACRODIR Overwrite the location where Autoconf files were installed. You can also set the @code{AC_MACRODIR} environment variable to a directory; this option overrides the environment variable. This option is rarely needed and dangerous: only when you play with different versions of Autoconf. @item --localdir=@var{dir} @itemx -l @var{dir} Look for the package file @file{aclocal.m4} in directory @var{dir} instead of in the current directory. @item --output=@var{file} @itemx -o @var{file} Save output (script or trace) to @var{file}. The file @option{-} stands for the standard output. @item --warnings=@var{category} @itemx -W @var{category} @evindex WARNINGS Report the warnings related to @var{category} (which can actually be a comma separated list). @xref{Reporting Messages}, macro @code{AC_DIAGNOSE}, for a comprehensive list of categories. Special values include: @table @samp @item all report all the warnings @item none report none @item error treats warnings as errors @item no-@var{category} disable warnings falling into @var{category} @end table Warnings about @samp{syntax} are enabled by default, and the environment variable @code{WARNINGS}, a comma separated list of categories, is honored. @command{autoconf} will actually behave as if you had run @example autoconf --warnings=syntax,$WARNINGS,@var{categories} @end example @noindent If you want to disable @command{autoconf}'s defaults and @code{WARNING} but enable the warnings about obsolete constructs, use @samp{-W none,obsolete}. @item --trace=@var{macro}[:@var{format}] @itemx -t @var{macro}[:@var{format}] Do not create the @code{configure} script, but list the calls to @var{macro} according to the @var{format}. Multiple @option{--trace} list several macros. Multiple @option{--trace} for a single macro do not accumulate, nevertheless, @var{format} can be arbitrarily long. The @var{format} is a regular string, with new lines if wanted. It defaults to @samp{$f:$l:$n:$%}, see below for details on the @var{format}. @item --initialization @itemx -i By default @option{--trace} does not trace the initialization of the Autoconf macros (typically the @code{AC_DEFUN} definitions). This results in a noticeable speedup, but can be disabled by this option. @end table It is often necessary to check the content of a @file{configure.in} file, but it is extremely fragile and error prone to try to parse it. It is suggested to rely upon @option{--trace} to scan @file{configure.in}. The @var{format} of @option{--trace} can use the following special escapes: @table @samp @item $$ The character @samp{$}. @item $f The filename from where @var{macro} is called. @item $l The line number from where @var{macro} is called. @item $d The depth of the @var{macro} call. This is an M4 technical detail which you probably don't want to know about. @item $n The name of the @var{macro}. @item $@var{num} The @var{num}th argument of the call to @var{macro}. @item $@@ @itemx $@var{sep}@@ @itemx $@{@var{separator}@}@@ All the arguments given to the @var{macro} separated by the character @var{sep} or the string @var{separator}, @samp{,} by default. Each argument is quoted, i.e. enclosed in a pair of square bracket. @item $* @itemx $@var{sep}* @itemx $@{@var{separator}@}* As above, but the arguments are not quoted. @item $% @itemx $@var{sep}% @itemx $@{@var{separator}@}% As above, but the arguments are not quoted, all new line characters in the arguments are smashed, and the default separator is @samp{:}. The escape @samp{$%} produces traces that hold in a single line (unless you put new lines in the @samp{separator}), while @samp{$@@} and @samp{$*} do not. @end table For instance, to know the list of variables that are substituted: @example @group % autoconf -t AC_SUBST configure.in:2:AC_SUBST:ECHO_C configure.in:2:AC_SUBST:ECHO_N configure.in:2:AC_SUBST:ECHO_T @i{More traces deleted} @end group @end example @noindent The example below highlights the difference between @samp{$@@}, @samp{$*}, and @strong{$%}. @example @group % cat configure.in AC_DEFINE(This, is, [an [example]]) % autoconf -t 'AC_DEFINE:@@: $@@ *: $* %: $%' @@: [This],[is],[an [example]] *: This,is,an [example] %: This:is:an [example] @end group @end example @noindent Much freedom is given over the @var{format}: @example @group % autoconf -t 'AC_SUBST:ac_subst@{"$1"@} = "$f:$l";' ac_subst@{"ECHO_C"@} = "configure.in:2"; ac_subst@{"ECHO_N"@} = "configure.in:2"; ac_subst@{"ECHO_T"@} = "configure.in:2"; @i{More traces deleted} @end group @end example @noindent The long @var{separator}s can be used to ease parsing of complex structures: @example @group % autoconf -t 'AM_MISSING_PROG:$@{|:::::|@}*' ACLOCAL|:::::|aclocal|:::::|$missing_dir AUTOCONF|:::::|autoconf|:::::|$missing_dir AUTOMAKE|:::::|automake|:::::|$missing_dir @i{More traces deleted} @end group @end example @node autoreconf Invocation, , autoconf Invocation, Making configure Scripts @section Using @code{autoreconf} to Update @code{configure} Scripts @cindex @code{autoreconf} If you have a lot of Autoconf-generated @code{configure} scripts, the @code{autoreconf} program can save you some work. It runs @code{autoconf} (and @code{autoheader}, where appropriate) repeatedly to remake the Autoconf @code{configure} scripts and configuration header templates in the directory tree rooted at the current directory. By default, it only remakes those files that are older than their @file{configure.in} or (if present) @file{aclocal.m4}. Since @code{autoheader} does not change the timestamp of its output file if the file wouldn't be changing, this is not necessarily the minimum amount of work. If you install a new version of Autoconf, you can make @code{autoreconf} remake @emph{all} of the files by giving it the @option{--force} option. If you give @code{autoreconf} the @option{--autoconf-dir=@var{dir}} or @option{--localdir=@var{dir}} options, it passes them down to @code{autoconf} and @code{autoheader} (with relative paths adjusted properly). @code{autoreconf} does not support having, in the same directory tree, both directories that are parts of a larger package (sharing @file{aclocal.m4} and @file{acconfig.h}), and directories that are independent packages (each with their own @file{aclocal.m4} and @file{acconfig.h}). It assumes that they are all part of the same package, if you use @option{--localdir}, or that each directory is a separate package, if you don't use it. This restriction may be removed in the future. @xref{Automatic Remaking}, for @file{Makefile} rules to automatically remake @code{configure} scripts when their source files change. That method handles the timestamps of configuration header templates properly, but does not pass @option{--autoconf-dir=@var{dir}} or @option{--localdir=@var{dir}}. @noindent @code{autoreconf} accepts the following options: @table @option @item --help @itemx -h Print a summary of the command line options and exit. @item --version @itemx -V Print the version number of Autoconf and exit. @item --verbose Print the name of each directory where @code{autoreconf} runs @code{autoconf} (and @code{autoheader}, if appropriate). @item --debug @itemx -d Don't remove the temporary files. @item --force @itemx -f Remake even @file{configure} scripts and configuration headers that are newer than their input files (@file{configure.in} and, if present, @file{aclocal.m4}). @item --localdir=@var{dir} @itemx -l @var{dir} Have @code{autoconf} and @code{autoheader} look for the package files @file{aclocal.m4} and (@code{autoheader} only) @file{acconfig.h} (but not @file{@var{file}.top} and @file{@var{file}.bot}) in directory @var{dir} instead of in the directory containing each @file{configure.in}. @item --autoconf-dir=@var{dir} @itemx -A @evindex AC_MACRODIR Overwrite the location where Autoconf files were installed. You can also set the @code{AC_MACRODIR} environment variable to a directory; this option overrides the environment variable. This option is rarely needed and dangerous: only when you play with different versions of Autoconf. @end table @c ========================================= Initialization and Output Files. @node Setup, Existing Tests, Making configure Scripts, Top @chapter Initialization and Output Files Autoconf-generated @code{configure} scripts need some information about how to initialize, such as how to find the package's source files; and about the output files to produce. The following sections describe initialization and creating output files. @menu * Notices:: Copyright, version numbers in @code{configure} * Input:: Where Autoconf should find files * Output:: Outputting results from the configuration * Configuration Actions:: Preparing the output based on results * Configuration Files:: Creating output files * Makefile Substitutions:: Using output variables in @file{Makefile}s * Configuration Headers:: Creating a configuration header file * Configuration Commands:: Running arbitrary instantiation commands * Configuration Links:: Links depending from the configuration * Subdirectories:: Configuring independent packages together * Default Prefix:: Changing the default installation prefix @end menu @node Notices, Input, Setup, Setup @section Notices in @code{configure} The following macros manage version numbers for @code{configure} scripts. Using them is optional. @c FIXME: AC_PREREQ should not be here, but where should it go? @defmac AC_PREREQ (@var{version}) @maindex PREREQ @cindex Version Ensure that a recent enough version of Autoconf is being used. If the version of Autoconf being used to create @code{configure} is earlier than @var{version}, print an error message on the standard error output and do not create @code{configure}. For example: @example AC_PREREQ(@value{VERSION}) @end example This macro is the only macro that may be used before @code{AC_INIT}, but for consistency, you are invited not to do so. @end defmac @defmac AC_COPYRIGHT (@var{copyright-notice}) @maindex COPYRIGHT @cindex Copyright Notice State that in addition to the Free Software Foundation's copyright over the Autoconf macros, parts of your @code{configure} are covered by the @var{copyright-notice}. The @var{copyright-notice} will show up in both the head of @code{configure}, and in @samp{configure --version}. @end defmac @defmac AC_REVISION (@var{revision-info}) @maindex REVISION @cindex Revision Copy revision stamp @var{revision-info} into the @code{configure} script, with any dollar signs or double-quotes removed. This macro lets you put a revision stamp from @file{configure.in} into @code{configure} without @sc{rcs} or @code{cvs} changing it when you check in @code{configure}. That way, you can determine easily which revision of @file{configure.in} a particular @code{configure} corresponds to. For example, this line in @file{configure.in}: @c The asis prevents RCS from changing the example in the manual. @example AC_REVISION($@asis{Revision: 1.30 }$) @end example @noindent produces this in @code{configure}: @example #! /bin/sh # From configure.in Revision: 1.30 @end example @end defmac @node Input, Output, Notices, Setup @section Finding @code{configure} Input Every @code{configure} script must call @code{AC_INIT} before doing anything else. The only other required macro is @code{AC_OUTPUT} (@pxref{Output}). @defmac AC_INIT (@var{package}, @var{version}, @ovar{bug-report-address}) @maindex INIT Process any command-line arguments and perform various initializations and verifications. Set the name of the @var{package} and its @var{version}. The optional argument @var{bug-report-address} should be the email to which users should send bug reports. @end defmac @defmac AC_CONFIG_SRCDIR (@var{unique-file-in-source-dir}) @maindex CONFIG_SRCDIR @var{unique-file-in-source-dir} is some file that is in the package's source directory; @code{configure} checks for this file's existence to make sure that the directory that it is told contains the source code in fact does. Occasionally people accidentally specify the wrong directory with @option{--srcdir}; this is a safety check. @xref{configure Invocation}, for more information. @end defmac @c FIXME: Remove definitively once --install explained. @c @c Small packages may store all their macros in @code{aclocal.m4}. As the @c set of macros grows, or for maintenance reasons, a maintainer may prefer @c to split the macros in several files. In this case, Autoconf must be @c told which files to load, and in which order. @c @c @defmac AC_INCLUDE (@var{file}...) @c @maindex INCLUDE @c @c FIXME: There is no longer shell globbing. @c Read the macro definitions that appear in the listed files. A list of @c space-separated filenames or shell globbing patterns is expected. The @c files will be read in the order they're listed. @c @c Because the order of definition of macros is important (only the last @c definition of a macro is used), beware that it is @code{AC_INIT} that @c loads @file{acsite.m4} and @file{aclocal.m4}. Note that @c @code{AC_INCLUDE}ing a file before @code{AC_INIT} or within @c @file{aclocal.m4} is different from doing so after @code{AC_INIT}: in @c the latter case, non-macro lines from included files may end up in the @c @file{configure} script, whereas in the former case, they'd be discarded @c just like any text that appear before @code{AC_INIT}. @c @end defmac Packages that do manual configuration or use the @code{install} program might need to tell @code{configure} where to find some other shell scripts by calling @code{AC_CONFIG_AUX_DIR}, though the default places it looks are correct for most cases. @defmac AC_CONFIG_AUX_DIR (@var{dir}) @maindex CONFIG_AUX_DIR Use the @file{install-sh}, @file{config.sub}, @file{config.guess}, and Cygnus @code{configure} scripts that are in directory @var{dir}. These are auxiliary files used in configuration. @var{dir} can be either absolute or relative to @file{@var{srcdir}}. The default is @file{@var{srcdir}} or @file{@var{srcdir}/..} or @file{@var{srcdir}/../..}, whichever is the first that contains @file{install-sh}. The other files are not checked for, so that using @code{AC_PROG_INSTALL} does not automatically require distributing the other auxiliary files. It checks for @file{install.sh} also, but that name is obsolete because some @code{make} programs have a rule that creates @file{install} from it if there is no @file{Makefile}. @end defmac @node Output, Configuration Actions, Input, Setup @section Outputting Files Every Autoconf-generated @code{configure} script must finish by calling @code{AC_OUTPUT}. It is the macro that generates @file{config.status} which will create the @file{Makefile}s and optional other files resulting from configuration. The only other required macro is @code{AC_INIT} (@pxref{Input}). Because of history, this macro is described twice below. The first definition describes the use that is now recommended. The second describes the former use, and its modern equivalent. @defmac AC_OUTPUT @maindex OUTPUT @cindex Instantiation Generate @file{config.status} and launch it. Call this macro once, at the end of @file{configure.in}. @file{config.status} will take all the configuration actions: all the output files (see @ref{Configuration Files}, macro @code{AC_CONFIG_FILES}), header files (see @ref{Configuration Headers}, macro @code{AC_CONFIG_HEADERS}), commands (see @ref{Configuration Commands}, macro @code{AC_CONFIG_COMMANDS}), links (see @ref{Configuration Links}, macro @code{AC_CONFIG_LINKS}), subdirectories to configure (see @ref{Subdirectories}, macro @code{AC_CONFIG_SUBDIRS}) are honored. @end defmac @xref{Obsolete Macros}, for a description of the arguments @code{AC_OUTPUT} used to support. If you run @code{make} on subdirectories, you should run it using the @code{make} variable @code{MAKE}. Most versions of @code{make} set @code{MAKE} to the name of the @code{make} program plus any options it was given. (But many do not include in it the values of any variables set on the command line, so those are not passed on automatically.) Some old versions of @code{make} do not set this variable. The following macro allows you to use it even with those versions. @defmac AC_PROG_MAKE_SET @maindex PROG_MAKE_SET @ovindex SET_MAKE If @code{make} predefines the variable @code{MAKE}, define output variable @code{SET_MAKE} to be empty. Otherwise, define @code{SET_MAKE} to contain @samp{MAKE=make}. Calls @code{AC_SUBST} for @code{SET_MAKE}. @end defmac To use this macro, place a line like this in each @file{Makefile.in} that runs @code{MAKE} on other directories: @example @@SET_MAKE@@ @end example @node Configuration Actions, Configuration Files, Output, Setup @section Taking Configuration Actions While everything is made so that you imagine @file{configure} does everything by itself, there is actually a hidden slave: @file{config.status}. @file{configure} is in charge of examining your system, but it is @file{config.status} that actually takes the proper actions based on the results of @file{configure}. The most typical task of @file{config.status} is to @emph{instantiate} files. This section describes the common behavior of the four standard instantiating macros: @code{AC_CONFIG_FILES}, @code{AC_CONFIG_HEADERS}, macro @code{AC_CONFIG_COMMANDS}, and @code{AC_CONFIG_LINKS}. They all have this prototype: @c Can't use @ovar here, Texinfo 4.0 goes lunatic and emits something @c awful. @example AC_CONFIG_FOOS(@var{tag}..., [@var{commands}], [@var{init-cmds}]) @end example @noindent where the arguments are: @table @var @item @var{tag}@dots{} A whitespace-separated list of tags, which are typically the names of the files to instantiate. @item commands They are output into @file{config.status} as literally. These commands are always associated to a tag which the user can use to tell @file{config.status} what are the commands she wants to run. These commands are run each time a @var{tag} request is given to @file{config.status}, i.e., typically each time the file @file{@var{tag}} is created. @item init-cmds They are output via an @emph{unquoted} here-doc. As a consequence @samp{$var} will be output as the value of @var{var}. This is typically used by @file{configure} to give @file{config.status} some variables it needs to run the @var{cmds}. At the difference of @var{cmds}, the @var{init-cmds} are always run. @end table All these macros can be called multiple times, with different @var{tag}s, of course! You are encouraged to use literals as @var{tags}. In particular, you should avoid @example ... && my_foos="$my_foos fooo" ... && my_foos="$my_foos foooo" AC_CONFIG_FOOS($my_foos) @end example @noindent and use this instead: @example ... && AC_CONFIG_FOOS(fooo) ... && AC_CONFIG_FOOS(foooo) @end example The macro @code{AC_CONFIG_FILES} and @code{AC_CONFIG_HEADERS} use specials @var{tag}s: they may have the form @samp{@var{output}} or @samp{@var{output}:@var{inputs}}. The file @var{output} is instantiated from its templates, @var{inputs} if specified, defaulting to @samp{@var{output}.in}. For instance @samp{AC_CONFIG_FILES(Makefile:boiler/top.mk:boiler/bot.mk)} asks for the creation of @file{Makefile} that will be the expansion of the output variables in the concatenation of @file{boiler/top.mk} and @file{boiler/bot.mk}. The special value @samp{-} might be used to denote the standard output when used in @var{output}, or the standard input when used in the @var{inputs}. You most probably don't need to use this in @file{configure.in}, but it is convenient when using the command line interface of @file{./config.status}, see @ref{config.status Invocation}, for more details. The @var{inputs} may be absolute or relative filenames. In the latter case they are first looked for in the build tree, and then in the source tree. @node Configuration Files, Makefile Substitutions, Configuration Actions, Setup @section Creating Configuration Files Be sure to read the previous section, @ref{Configuration Actions}. @defmac AC_CONFIG_FILES (@var{file}@dots{}, @ovar{cmds}, @ovar{init-cmds}) @maindex CONFIG_FILES Make @code{AC_OUTPUT} create each @file{@var{file}} by copying an input file (by default @file{@var{file}.in}), substituting the output variable values. @c FIXME: Before we used to have this feature, which was later rejected @c because it complicates the write of Makefiles: @c If the file would be unchanged, it is left untouched, to preserve @c timestamp. This macro is one of the instantiating macros, see @ref{Configuration Actions}. @xref{Makefile Substitutions}, for more information on using output variables. @xref{Setting Output Variables}, for more information on creating them. This macro creates the directory that the file is in if it doesn't exist. Usually, @file{Makefile}s are created this way, but other files, such as @file{.gdbinit}, can be specified as well. Typical calls to @code{AC_CONFIG_FILES} look like this: @example AC_CONFIG_FILES(Makefile src/Makefile man/Makefile X/Imakefile) AC_CONFIG_FILES(autoconf, chmod +x autoconf) @end example You can override an input file name by appending to @var{file} a colon-separated list of input files. Examples: @example AC_CONFIG_FILES(Makefile:boiler/top.mk:boiler/bot.mk lib/Makefile:boiler/lib.mk) @end example @noindent Doing this allows you to keep your file names acceptable to MS-DOS, or to prepend and/or append boilerplate to the file. @end defmac @node Makefile Substitutions, Configuration Headers, Configuration Files, Setup @section Substitutions in Makefiles Each subdirectory in a distribution that contains something to be compiled or installed should come with a file @file{Makefile.in}, from which @code{configure} will create a @file{Makefile} in that directory. To create a @file{Makefile}, @code{configure} performs a simple variable substitution, replacing occurrences of @samp{@@@var{variable}@@} in @file{Makefile.in} with the value that @code{configure} has determined for that variable. Variables that are substituted into output files in this way are called @dfn{output variables}. They are ordinary shell variables that are set in @code{configure}. To make @code{configure} substitute a particular variable into the output files, the macro @code{AC_SUBST} must be called with that variable name as an argument. Any occurrences of @samp{@@@var{variable}@@} for other variables are left unchanged. @xref{Setting Output Variables}, for more information on creating output variables with @code{AC_SUBST}. A software package that uses a @code{configure} script should be distributed with a file @file{Makefile.in}, but no @file{Makefile}; that way, the user has to properly configure the package for the local system before compiling it. @xref{Makefile Conventions,, Makefile Conventions, standards, The GNU Coding Standards}, for more information on what to put in @file{Makefile}s. @menu * Preset Output Variables:: Output variables that are always set * Installation Directory Variables:: Other preset output variables * Build Directories:: Supporting multiple concurrent compiles * Automatic Remaking:: Makefile rules for configuring @end menu @node Preset Output Variables, Installation Directory Variables, Makefile Substitutions, Makefile Substitutions @subsection Preset Output Variables Some output variables are preset by the Autoconf macros. Some of the Autoconf macros set additional output variables, which are mentioned in the descriptions for those macros. @xref{Output Variable Index}, for a complete list of output variables. @xref{Installation Directory Variables}, for the list of the preset ones related to installation directories. Below are listed the other preset ones. @c Just say no to ASCII sorting! We're humans, not computers. @c These variables are listed as they would be in a dictionary: @c actor @c Actress @c actress @defvar CFLAGS @ovindex CFLAGS Debugging and optimization options for the C compiler. If it is not set in the environment when @code{configure} runs, the default value is set when you call @code{AC_PROG_CC} (or empty if you don't). @code{configure} uses this variable when compiling programs to test for C features. @end defvar @defvar configure_input @ovindex configure_input A comment saying that the file was generated automatically by @code{configure} and giving the name of the input file. @code{AC_OUTPUT} adds a comment line containing this variable to the top of every @file{Makefile} it creates. For other files, you should reference this variable in a comment at the top of each input file. For example, an input shell script should begin like this: @example #! /bin/sh # @@configure_input@@ @end example @noindent The presence of that line also reminds people editing the file that it needs to be processed by @code{configure} in order to be used. @end defvar @defvar CPPFLAGS @ovindex CPPFLAGS Header file search directory (@option{-I@var{dir}}) and any other miscellaneous options for the C and C++ preprocessors and compilers. If it is not set in the environment when @code{configure} runs, the default value is empty. @code{configure} uses this variable when compiling or preprocessing programs to test for C and C++ features. @end defvar @defvar CXXFLAGS @ovindex CXXFLAGS Debugging and optimization options for the C++ compiler. If it is not set in the environment when @code{configure} runs, the default value is set when you call @code{AC_PROG_CXX} (or empty if you don't). @code{configure} uses this variable when compiling programs to test for C++ features. @end defvar @defvar DEFS @ovindex DEFS @option{-D} options to pass to the C compiler. If @code{AC_CONFIG_HEADERS} is called, @code{configure} replaces @samp{@@DEFS@@} with @option{-DHAVE_CONFIG_H} instead (@pxref{Configuration Headers}). This variable is not defined while @code{configure} is performing its tests, only when creating the output files. @xref{Setting Output Variables}, for how to check the results of previous tests. @end defvar @defvar ECHO_C @defvarx ECHO_N @defvarx ECHO_T @ovindex ECHO_C @ovindex ECHO_N @ovindex ECHO_T How to suppress the trailing newline from @code{echo} for question... answer reports: @example echo $ECHO_N "And the winner is... $ECHO_C" sleep 100000000000 echo "$@{ECHO_T@}dead." @end example @noindent Some old and uncommon @code{echo} offer no means to achieve this, in which case @code{ECHO_T} is set to tab. You might not want to use it. @end defvar @defvar FFLAGS @ovindex FFLAGS Debugging and optimization options for the Fortran 77 compiler. If it is not set in the environment when @code{configure} runs, the default value is set when you call @code{AC_PROG_F77} (or empty if you don't). @code{configure} uses this variable when compiling programs to test for Fortran 77 features. @end defvar @defvar LDFLAGS @ovindex LDFLAGS Stripping (@option{-s}), path (@option{-L}), and any other miscellaneous options for the linker. Don't use this variable to pass library names (@option{-l}) to the linker, use @code{LIBS} instead. If it is not set in the environment when @code{configure} runs, the default value is empty. @code{configure} uses this variable when linking programs to test for C, C++ and Fortran 77 features. @end defvar @defvar LIBS @ovindex LIBS @option{-l} options to pass to the linker. The default value is empty, but some Autoconf macros may prepend extra libraries to this variable if those libraries are found and provide necessary functions, see @ref{Libraries}. @code{configure} uses this variable when linking programs to test for C, C++ and Fortran 77 features. @end defvar @defvar srcdir @ovindex srcdir The directory that contains the source code for that @file{Makefile}. @end defvar @defvar top_srcdir @ovindex top_srcdir The top-level source code directory for the package. In the top-level directory, this is the same as @code{srcdir}. @end defvar @node Installation Directory Variables, Build Directories, Preset Output Variables, Makefile Substitutions @subsection Installation Directory Variables The following variables specify the directories where the package will be installed, see @ref{Directory Variables,, Variables for Installation Directories, standards, The GNU Coding Standards}, for more information. See the end of this section for details on when and how to use these variables. @defvar bindir @ovindex bindir The directory for installing executables that users run. @end defvar @defvar datadir @ovindex datadir The directory for installing read-only architecture-independent data. @end defvar @defvar exec_prefix @ovindex exec_prefix The installation prefix for architecture-dependent files. @end defvar @defvar includedir @ovindex includedir The directory for installing C header files. @end defvar @defvar infodir @ovindex infodir The directory for installing documentation in Info format. @end defvar @defvar libdir @ovindex libdir The directory for installing object code libraries. @end defvar @defvar libexecdir @ovindex libexecdir The directory for installing executables that other programs run. @end defvar @defvar localstatedir @ovindex localstatedir The directory for installing modifiable single-machine data. @end defvar @defvar mandir @ovindex mandir The top-level directory for installing documentation in man format. @end defvar @defvar oldincludedir @ovindex oldincludedir The directory for installing C header files for non-gcc compilers. @end defvar @defvar prefix @ovindex prefix The installation prefix for architecture-independent files. @end defvar @defvar sbindir @ovindex sbindir The directory for installing executables that system administrators run. @end defvar @defvar sharedstatedir @ovindex sharedstatedir The directory for installing modifiable architecture-independent data. @end defvar @defvar sysconfdir @ovindex sysconfdir The directory for installing read-only single-machine data. @end defvar Most of these variables have values that rely on @code{prefix} or @code{exec_prefix}. It is on purpose that the directory output variables keep them unexpanded: typically @samp{@@datadir@@} will be replaced by @samp{$@{prefix@}/share}, not @samp{/usr/local/share}. This behavior is mandated by the @sc{gnu} coding standards, so that when the user runs: @table @samp @item make she can still specify a different prefix from the one specified to @command{configure}, in which case, if needed, the package shall hard code dependencies to her late desires. @item make install she can specify a different installation location, in which case the package @emph{must} still depend on the location which was compiled in (i.e., never recompile when @samp{make install} is run). This is an extremely important feature, as many people may decide to install all the files of a package grouped together, and then install links from the final locations to there. @end table In order to support these features, it is essential that @code{datadir} remains being defined as @samp{$@{prefix@}/share} to depend upon the current value of @code{prefix}. A corollary is that you should not use these variables but in Makefiles. For instance instead of trying to resolve the dependencies of @code{datadir} upon @code{prefix} and using @samp{AC_DEFINE_UNQUOTED(DATADIR, "$datadir")}, you should add @samp{-DDATADIR="$(datadir)"} to your @code{CFLAGS}. Similarly you should not rely on @code{AC_OUTPUT_FILES} to replace @code{datadir} and friends in your shell scripts and other files, rather let @command{make} manage their replacement. For instance Autoconf ships templates of its shell scripts ending with @samp{.sh}, and uses this Makefile snippet: @example .sh: rm -f $@@ $@@.tmp sed 's,@@datadir\@@,$(pkgdatadir),g' $< >$@@.tmp chmod +x $@@.tmp mv $@@.tmp $@@ @end example Three things are noteworthy: @table @samp @item @@datadir\@@ The backslash prevents @command{configure} from replacing @samp{@@datadir@@} in the sed expression itself. @item $(pkgdatadir) Don't use @samp{@@pkgdatadir@@}! Use the matching makefile variable instead. @item , Don't use @samp{/} in the sed expression(s) since most probably the variables you use, such as @samp{$(pkgdatadir)}, will contain some. @end table @node Build Directories, Automatic Remaking, Installation Directory Variables, Makefile Substitutions @subsection Build Directories You can support compiling a software package for several architectures simultaneously from the same copy of the source code. The object files for each architecture are kept in their own directory. To support doing this, @code{make} uses the @code{VPATH} variable to find the files that are in the source directory. @sc{gnu} @code{make} and most other recent @code{make} programs can do this. Older @code{make} programs do not support @code{VPATH}; when using them, the source code must be in the same directory as the object files. To support @code{VPATH}, each @file{Makefile.in} should contain two lines that look like: @example srcdir = @@srcdir@@ VPATH = @@srcdir@@ @end example Do not set @code{VPATH} to the value of another variable, for example @samp{VPATH = $(srcdir)}, because some versions of @code{make} do not do variable substitutions on the value of @code{VPATH}. @code{configure} substitutes in the correct value for @code{srcdir} when it produces @file{Makefile}. Do not use the @code{make} variable @code{$<}, which expands to the file name of the file in the source directory (found with @code{VPATH}), except in implicit rules. (An implicit rule is one such as @samp{.c.o}, which tells how to create a @file{.o} file from a @file{.c} file.) Some versions of @code{make} do not set @code{$<} in explicit rules; they expand it to an empty value. Instead, @file{Makefile} command lines should always refer to source files by prefixing them with @samp{$(srcdir)/}. For example: @example time.info: time.texinfo $(MAKEINFO) $(srcdir)/time.texinfo @end example @node Automatic Remaking, , Build Directories, Makefile Substitutions @subsection Automatic Remaking You can put rules like the following in the top-level @file{Makefile.in} for a package to automatically update the configuration information when you change the configuration files. This example includes all of the optional files, such as @file{aclocal.m4} and those related to configuration header files. Omit from the @file{Makefile.in} rules for any of these files that your package does not use. The @samp{$(srcdir)/} prefix is included because of limitations in the @code{VPATH} mechanism. The @file{stamp-} files are necessary because the timestamps of @file{config.h.in} and @file{config.h} will not be changed if remaking them does not change their contents. This feature avoids unnecessary recompilation. You should include the file @file{stamp-h.in} your package's distribution, so @code{make} will consider @file{config.h.in} up to date. On some old @sc{bsd} systems, @code{touch} or any command that results in an empty file does not update the timestamps, so use a command like @code{echo} as a workaround. @c Using @code{date} would cause needless CVS conflicts. @example @group $(srcdir)/configure: configure.in aclocal.m4 cd $(srcdir) && autoconf # autoheader might not change config.h.in, so touch a stamp file. $(srcdir)/config.h.in: stamp-h.in $(srcdir)/stamp-h.in: configure.in aclocal.m4 acconfig.h \ config.h.top config.h.bot cd $(srcdir) && autoheader echo timestamp > $(srcdir)/stamp-h.in config.h: stamp-h stamp-h: config.h.in config.status ./config.status Makefile: Makefile.in config.status ./config.status config.status: configure ./config.status --recheck @end group @end example In addition, you should use @samp{AC_CONFIG_FILES(stamp-h, echo timestamp > stamp-h)} so @file{config.status} will ensure that @file{config.h} is considered up to date. @xref{Output}, for more information about @code{AC_OUTPUT}. @xref{config.status Invocation}, for more examples of handling configuration-related dependencies. @node Configuration Headers, Configuration Commands, Makefile Substitutions, Setup @section Configuration Header Files @cindex Configuration Header @cindex @file{config.h} When a package tests more than a few C preprocessor symbols, the command lines to pass @option{-D} options to the compiler can get quite long. This causes two problems. One is that the @code{make} output is hard to visually scan for errors. More seriously, the command lines can exceed the length limits of some operating systems. As an alternative to passing @option{-D} options to the compiler, @code{configure} scripts can create a C header file containing @samp{#define} directives. The @code{AC_CONFIG_HEADERS} macro selects this kind of output. It should be called right after @code{AC_INIT}. The package should @samp{#include} the configuration header file before any other header files, to prevent inconsistencies in declarations (for example, if it redefines @code{const}). Use @samp{#include } instead of @samp{#include "config.h"}, and pass the C compiler a @option{-I.} option (or @option{-I..}; whichever directory contains @file{config.h}). That way, even if the source directory is configured itself (perhaps to make a distribution), other build directories can also be configured without finding the @file{config.h} from the source directory. @defmac AC_CONFIG_HEADERS (@var{header} @dots{}, @ovar{cmds}, @ovar{init-cmds}) @maindex CONFIG_HEADERS @cvindex HAVE_CONFIG_H This macro is one of the instantiating macros, see @ref{Configuration Actions}. Make @code{AC_OUTPUT} create the file(s) in the whitespace-separated list @var{header} containing C preprocessor @code{#define} statements, and replace @samp{@@DEFS@@} in generated files with @option{-DHAVE_CONFIG_H} instead of the value of @code{DEFS}. The usual name for @var{header} is @file{config.h}. If @var{header} already exists and its contents are identical to what @code{AC_OUTPUT} would put in it, it is left alone. Doing this allows some changes in configuration without needlessly causing object files that depend on the header file to be recompiled. Usually the input file is named @file{@var{header}.in}; however, you can override the input file name by appending to @var{header}, a colon-separated list of input files. Examples: @example AC_CONFIG_HEADERS(config.h:config.hin) AC_CONFIG_HEADERS(defines.h:defs.pre:defines.h.in:defs.post) @end example @noindent Doing this allows you to keep your file names acceptable to MS-DOS, or to prepend and/or append boilerplate to the file. @end defmac @xref{Configuration Actions}, for more details on @var{header}. @menu * Header Templates:: Input for the configuration headers * autoheader Invocation:: How to create configuration templates * Autoheader Macros:: How to specify CPP templates @end menu @node Header Templates, autoheader Invocation, Configuration Headers, Configuration Headers @subsection Configuration Header Templates @cindex Configuration Header Template @cindex @file{config.h.in} Your distribution should contain a template file that looks as you want the final header file to look, including comments, with @code{#undef} statements which are used as hooks. For example, suppose your @file{configure.in} makes these calls: @example AC_CONFIG_HEADERS(conf.h) AC_CHECK_HEADERS(unistd.h) @end example @noindent Then you could have code like the following in @file{conf.h.in}. On systems that have @file{unistd.h}, @code{configure} will @samp{#define} @samp{HAVE_UNISTD_H} to 1. On other systems, the whole line will be commented out (in case the system predefines that symbol). @example @group /* Define as 1 if you have unistd.h. */ #undef HAVE_UNISTD_H @end group @end example You can then decode the configuration header using the preprocessor directives: @example @group #include #if HAVE_UNISTD_H # include #else /* We are in trouble. */ #endif @end group @end example The use of old form templates, with @samp{#define} instead of @samp{#undef} is strongly discouraged. Since it is a tedious task to keep a template header up to date, you may use @code{autoheader} to generate it, see @ref{autoheader Invocation}. @node autoheader Invocation, Autoheader Macros, Header Templates, Configuration Headers @subsection Using @code{autoheader} to Create @file{config.h.in} @cindex @code{autoheader} The @command{autoheader} program can create a template file of C @samp{#define} statements for @code{configure} to use. If @file{configure.in} invokes @code{AC_CONFIG_HEADERS(@var{file})}, @command{autoheader} creates @file{@var{file}.in}; if multiple file arguments are given, the first one is used. Otherwise, @command{autoheader} creates @file{config.h.in}. In order to do its job @command{autoheader} needs that you document all the symbols that you might use, i.e., that there is at least one @code{AC_DEFINE} or one @code{AC_DEFINE_UNQUOTED} using its third argument, see @ref{Defining Symbols}. An additional constraint is that the first argument must be a literal. You might wonder why @command{autoheader} is needed: after all, why would @command{configure} need to ``patch'' a @file{config.h.in} to produce a @file{config.h} instead of just creating @file{config.h} from scratch? Well, when everything rocks the answer is just that we are losing our time maintaining @command{autoheader}: generating directly @file{config.h} is just what is needed. But when things go wrong, you'll thank the Autoconf team for @command{autoheader}... The fact that the symbols are documented is precious to @emph{check} that @file{config.h} makes sense. The fact that there is a well defined list of symbols that should be @code{#define}'d (or not) is also precious for people who are porting packages to environments where @command{configure} cannot be run: they just have to @emph{fill in the blanks}. But let's come back to the point: @command{autoheader}'s invocation... If you give @command{autoheader} an argument, it uses that file instead of @file{configure.in} and writes the header file to the standard output instead of to @file{config.h.in}. If you give @command{autoheader} an argument of @option{-}, it reads the standard input instead of @file{configure.in} and writes the header file to the standard output. @code{autoheader} accepts the following options: @table @option @item --help @itemx -h Print a summary of the command line options and exit. @item --version @itemx -V Print the version number of Autoconf and exit. @item --debug @itemx -d Don't remove the temporary files. @item --autoconf-dir=@var{dir} @itemx -A @evindex AC_MACRODIR Overwrite the location where Autoconf files were installed. You can also set the @code{AC_MACRODIR} environment variable to a directory; this option overrides the environment variable. This option is rarely needed and dangerous: only when you play with different versions of Autoconf. @item --localdir=@var{dir} @itemx -l @var{dir} Look for the package files @file{aclocal.m4} and @file{acconfig.h} (but not @file{@var{file}.top} and @file{@var{file}.bot}) in directory @var{dir} instead of in the current directory. @item --warnings=@var{category} @itemx -W @var{category} @evindex WARNINGS Report the warnings related to @var{category} (which can actually be a comma separated list). Current categories include: @table @samp @item obsolete report the uses of obsolete constructs @item all report all the warnings @item none report none @item error treats warnings as errors @item no-@var{category} disable warnings falling into @var{category} @end table @end table @node Autoheader Macros, , autoheader Invocation, Configuration Headers @subsection Autoheader Macros @code{autoheader} scans @file{configure.in} and figures out which C preprocessor symbols it might define. It knows how to generate templates for symbols defined by @code{AC_CHECK_HEADERS}, @code{AC_CHECK_FUNCS} etc., but if you @code{AC_DEFINE} any additional symbol, you must define a template for it. @code{autoheader} diagnoses missing templates, and fails. The simplest means to create a template for a @var{symbol} is simply to document one of the @samp{AC_DEFINE(@var{symbol})}, see @ref{Defining Symbols}. You may also use one of the following macros. @defmac AH_VERBATIM (@var{key}, @var{template}) @maindex AH_VERBATIM @maindex VERBATIM Inform @code{autoheader} that it must include the @var{template} as is in the header template file. This @var{template} is associated to the @var{key}, which is used to sort all the different templates, and guarantee their uniqueness. It should be the symbol that can be @code{AC_DEFINE}'d. For instance: @example AH_VERBATIM([_GNU_SOURCE], [/* Enable GNU extensions on systems that have them. */ #ifndef _GNU_SOURCE # define _GNU_SOURCE #endif]) @end example @end defmac @defmac AH_TEMPLATE (@var{key}, @var{description}) @maindex AH_TEMPLATE @maindex TEMPLATE Inform @code{autoheader} that it must generate a template for @var{key}. This macro generates standard templates, as @code{AC_DEFINE} does when a @var{description} is given. For instance: @example AH_TEMPLATE([CRAY_STACKSEG_END], [Define to one of _getb67, GETB67, getb67 for Cray-2 and Cray-YMP systems. This function is required for alloca.c support on those systems.]) @end example @noindent will generate the following template, with the description properly justified. @example /* Define to one of _getb67, GETB67, getb67 for Cray-2 and Cray-YMP systems. This function is required for alloca.c support on those systems. */ #undef CRAY_STACKSEG_END @end example @end defmac @defmac AH_TOP (@var{text}) @maindex AH_TOP @maindex TOP Include @var{text} at the top of the header template file. @end defmac @defmac AH_BOTTOM (@var{text}) @maindex AH_BOTTOM @maindex BOTTOM Include @var{text} at the bottom of the header template file. @end defmac @node Configuration Commands, Configuration Links, Configuration Headers, Setup @section Running Arbitrary Configuration Commands You execute arbitrary commands either before, during and after @file{config.status} is run. The three following macros accumulate the commands to run when they are called multiple times. @code{AC_CONFIG_COMMANDS} replaces the obsolete macro @code{AC_OUTPUT_COMMANDS}, see @ref{Obsolete Macros}, for details. @defmac AC_CONFIG_COMMANDS (@var{tag}@dots{}, @ovar{cmds}, @ovar{init-cmds}) @maindex CONFIG_COMMANDS Specify additional shell commands to run at the end of @file{config.status}, and shell commands to initialize any variables from @code{configure}. Associate the commands to the @var{tag}. Since typically the @var{cmds} create a file, @var{tag} should naturally be the name of that file. This macro is one of the instantiating macros, see @ref{Configuration Actions}. Here is an unrealistic example: @example fubar=42 AC_CONFIG_COMMANDS(fubar, [echo this is extra $fubar, and so on.], [fubar=$fubar]) @end example Here is a better one: @example AC_CONFIG_COMMANDS(time-stamp, [date >time-stamp]) @end example @end defmac @defmac AC_CONFIG_COMMANDS_PRE (@var{cmds}) @maindex OUTPUT_COMMANDS_PRE Execute the @var{cmds} right before creating @file{config.status}. A typical use is computing values derived from variables built during the execution of @code{configure}: @example AC_CONFIG_COMMANDS_PRE( [LTLIBOBJS=`echo $LIBOBJS | sed 's/\.o/\.lo/g'` AC_SUBST(LTLIBOBJS)]) @end example @end defmac @defmac AC_CONFIG_COMMANDS_POST (@var{cmds}) @maindex OUTPUT_COMMANDS_POST Execute the @var{cmds} right after creating @file{config.status}. @end defmac @node Configuration Links, Subdirectories, Configuration Commands, Setup @section Creating Configuration Links You may find it convenient to create links whose destinations depend upon results of tests. One can use @code{AC_CONFIG_COMMANDS} but the creation of relative symbolic links can be delicate when the package is built in another directory than its sources. @defmac AC_CONFIG_LINKS (@var{dest}:@var{source}@dots{}, @ovar{cmds}, @ovar{init-cmds}) @maindex CONFIG_LINKS @cindex Links Make @code{AC_OUTPUT} link each of the existing files @var{source} to the corresponding link name @var{dest}. Makes a symbolic link if possible, otherwise a hard link. The @var{dest} and @var{source} names should be relative to the top level source or build directory. This macro is one of the instantiating macros, see @ref{Configuration Actions}. For example, this call: @example AC_CONFIG_LINKS(host.h:config/$machine.h object.h:config/$obj_format.h) @end example @noindent creates in the current directory @file{host.h} as a link to @file{@var{srcdir}/config/$machine.h}, and @file{object.h} as a link to @file{@var{srcdir}/config/$obj_format.h}. The tempting value @samp{.} for @var{dest} is invalid: it makes it impossible for @samp{config.status} to guess the links to establish. It is then valid to run: @example ./config.status host.h object.h @end example to establish the links. @end defmac @node Subdirectories, Default Prefix, Configuration Links, Setup @section Configuring Other Packages in Subdirectories In most situations, calling @code{AC_OUTPUT} is sufficient to produce @file{Makefile}s in subdirectories. However, @code{configure} scripts that control more than one independent package can use @code{AC_CONFIG_SUBDIRS} to run @code{configure} scripts for other packages in subdirectories. @defmac AC_CONFIG_SUBDIRS (@var{dir} @dots{}) @maindex CONFIG_SUBDIRS @ovindex subdirs Make @code{AC_OUTPUT} run @code{configure} in each subdirectory @var{dir} in the given whitespace-separated list. Each @var{dir} should be a literal, i.e., please do not use: @example if test "$package_foo_enabled" = yes; then $my_subdirs="$my_subdirs foo" fi AC_CONFIG_SUBDIRS($my_subdirs) @end example @noindent because this prevents @samp{./configure --help=recursive} from displaying the options of the package @code{foo}. Rather, you should write: @example if test "$package_foo_enabled" = yes then; AC_CONFIG_SUBDIRS(foo) fi @end example If a given @var{dir} is not found, no error is reported, so a @code{configure} script can configure whichever parts of a large source tree are present. If a given @var{dir} contains @code{configure.gnu}, it is run instead of @code{configure}. This is for packages that might use a non-autoconf script @code{Configure}, which can't be called through a wrapper @code{configure} since it would be the same file on case-insensitive filesystems. Likewise, if a @var{dir} contains @file{configure.in} but no @code{configure}, the Cygnus @code{configure} script found by @code{AC_CONFIG_AUXDIR} is used. The subdirectory @code{configure} scripts are given the same command line options that were given to this @code{configure} script, with minor changes if needed (e.g., to adjust a relative path for the cache file or source directory). This macro also sets the output variable @code{subdirs} to the list of directories @samp{@var{dir} @dots{}}. @file{Makefile} rules can use this variable to determine which subdirectories to recurse into. This macro may be called multiple times. @end defmac @node Default Prefix, , Subdirectories, Setup @section Default Prefix By default, @code{configure} sets the prefix for files it installs to @file{/usr/local}. The user of @code{configure} can select a different prefix using the @option{--prefix} and @option{--exec-prefix} options. There are two ways to change the default: when creating @code{configure}, and when running it. Some software packages might want to install in a directory besides @file{/usr/local} by default. To accomplish that, use the @code{AC_PREFIX_DEFAULT} macro. @defmac AC_PREFIX_DEFAULT (@var{prefix}) Set the default installation prefix to @var{prefix} instead of @file{/usr/local}. @end defmac It may be convenient for users to have @code{configure} guess the installation prefix from the location of a related program that they have already installed. If you wish to do that, you can call @code{AC_PREFIX_PROGRAM}. @defmac AC_PREFIX_PROGRAM (@var{program}) @maindex PREFIX_PROGRAM If the user did not specify an installation prefix (using the @option{--prefix} option), guess a value for it by looking for @var{program} in @code{PATH}, the way the shell does. If @var{program} is found, set the prefix to the parent of the directory containing @var{program}; otherwise leave the prefix specified in @file{Makefile.in} unchanged. For example, if @var{program} is @code{gcc} and the @code{PATH} contains @file{/usr/local/gnu/bin/gcc}, set the prefix to @file{/usr/local/gnu}. @end defmac @c ======================================================== Existing tests @node Existing Tests, Writing Tests, Setup, Top @chapter Existing Tests These macros test for particular system features that packages might need or want to use. If you need to test for a kind of feature that none of these macros check for, you can probably do it by calling primitive test macros with appropriate arguments (@pxref{Writing Tests}). These tests print messages telling the user which feature they're checking for, and what they find. They cache their results for future @code{configure} runs (@pxref{Caching Results}). Some of these macros set output variables. @xref{Makefile Substitutions}, for how to get their values. The phrase ``define @var{name}'' is used below as a shorthand to mean ``define C preprocessor symbol @var{name} to the value 1''. @xref{Defining Symbols}, for how to get those symbol definitions into your program. @menu * Common Behavior:: Macros' standard schemes * Alternative Programs:: Selecting between alternative programs * Libraries:: Library archives that might be missing * Library Functions:: C library functions that might be missing * Header Files:: Header files that might be missing * Declarations:: Declarations that may be missing * Structures:: Structures or members that might be missing * Types:: Types that might be missing * Compilers and Preprocessors:: Checking for compiling programs * C Compiler Characteristics:: * Fortran 77 Compiler Characteristics:: * System Services:: Operating system services * UNIX Variants:: Special kludges for specific UNIX variants @end menu @node Common Behavior, Alternative Programs, Existing Tests, Existing Tests @section Common Behavior Much effort was put into Autoconf to make it easy to learn. The most obvious way to reach this goal is simply to enforce standard and rigorous schemes, and to avoid as much as possible exceptions. Because of history and momentum, there are still too many exceptions in Autoconf, nevertheless this section describes some of the common rules. @menu * Standard Symbols:: Symbols defined by the macros * Default Includes:: Includes used by the generic macros @end menu @node Standard Symbols, Default Includes, Common Behavior, Common Behavior @subsection Standard Symbols All the generic macros that @code{AC_DEFINE} a symbol as a result of their test transform their @var{argument}s to a standard alphabet. First, @var{argument} is mapped to upper case and any star @samp{*} to @samp{P}. Any characters that remain that are not alpha-numerical or underscores are mapped to underscores. For instance @example AC_CHECK_TYPES(struct $Expensive*) @end example @noindent may define the symbol @samp{HAVE_STRUCT__EXPENSIVEP}. @node Default Includes, , Standard Symbols, Common Behavior @subsection Default Includes @cindex Includes, default Several tests depend upon a set of headers. Since headers are not universally available, you actually have to provide a set of protected includes, such as @example @group #if TIME_WITH_SYS_TIME # include # include #else # if HAVE_SYS_TIME_H # include # else # include # endif #endif @end group @end example @noindent Unless you know exactly what you are doing, you should avoid using unconditional includes, and check the existence of the headers you include beforehand (@pxref{Header Files}). Most generic macros provide the following default set of includes: @example @group #include #include #if STDC_HEADERS # include # include #else # if HAVE_STDLIB_H # include # endif #endif #if HAVE_STRING_H # if !STDC_HEADERS && HAVE_MEMORY_H # include # endif # include #else # if HAVE_STRINGS_H # include # endif #endif #if HAVE_INTTYPES_H # include #endif #if HAVE_UNISTD_H # include #endif @end group @end example @node Alternative Programs, Libraries, Common Behavior, Existing Tests @section Alternative Programs @cindex Programs, checking These macros check for the presence or behavior of particular programs. They are used to choose between several alternative programs and to decide what to do once one has been chosen. If there is no macro specifically defined to check for a program you need, and you don't need to check for any special properties of it, then you can use one of the general program check macros. @menu * Particular Programs:: Special handling to find certain programs * Generic Programs:: How to find other programs @end menu @node Particular Programs, Generic Programs, Alternative Programs, Alternative Programs @subsection Particular Program Checks These macros check for particular programs---whether they exist, and in some cases whether they support certain features. @defmac AC_PROG_AWK @maindex PROG_AWK @ovindex AWK Check for @code{mawk}, @code{gawk}, @code{nawk}, and @code{awk}, in that order, and set output variable @code{AWK} to the first one that is found. It tries @code{mawk} first because that is reported to be the fastest implementation. @end defmac @defmac AC_PROG_INSTALL @maindex PROG_INSTALL @ovindex INSTALL @ovindex INSTALL_PROGRAM @ovindex INSTALL_DATA @ovindex INSTALL_SCRIPT Set output variable @code{INSTALL} to the path of a @sc{bsd} compatible @code{install} program, if one is found in the current @code{PATH}. Otherwise, set @code{INSTALL} to @samp{@var{dir}/install-sh -c}, checking the directories specified to @code{AC_CONFIG_AUX_DIR} (or its default directories) to determine @var{dir} (@pxref{Output}). Also set the variables @code{INSTALL_PROGRAM} and @code{INSTALL_SCRIPT} to @samp{$@{INSTALL@}} and @code{INSTALL_DATA} to @samp{$@{INSTALL@} -m 644}. This macro screens out various instances of @code{install} known not to work. It prefers to find a C program rather than a shell script, for speed. Instead of @file{install-sh}, it can also use @file{install.sh}, but that name is obsolete because some @code{make} programs have a rule that creates @file{install} from it if there is no @file{Makefile}. A copy of @file{install-sh} which you may use comes with Autoconf. If you use @code{AC_PROG_INSTALL}, you must include either @file{install-sh} or @file{install.sh} in your distribution, or @code{configure} will produce an error message saying it can't find them---even if the system you're on has a good @code{install} program. This check is a safety measure to prevent you from accidentally leaving that file out, which would prevent your package from installing on systems that don't have a @sc{bsd}-compatible @code{install} program. If you need to use your own installation program because it has features not found in standard @code{install} programs, there is no reason to use @code{AC_PROG_INSTALL}; just put the file name of your program into your @file{Makefile.in} files. @end defmac @defmac AC_PROG_LEX @maindex PROG_LEX @ovindex LEX @ovindex LEXLIB @cvindex YYTEXT_POINTER @ovindex LEX_OUTPUT_ROOT If @code{flex} is found, set output variable @code{LEX} to @samp{flex} and @code{LEXLIB} to @option{-lfl}, if that library is in a standard place. Otherwise set @code{LEX} to @samp{lex} and @code{LEXLIB} to @option{-ll}. Define @code{YYTEXT_POINTER} if @code{yytext} is a @samp{char *} instead of a @samp{char []}. Also set output variable @code{LEX_OUTPUT_ROOT} to the base of the file name that the lexer generates; usually @file{lex.yy}, but sometimes something else. These results vary according to whether @code{lex} or @code{flex} is being used. You are encouraged to use Flex in your sources, since it is both more pleasant to use than plain Lex, and the C source it produces is portable. But in order to ensure portability, you must either provide a function @code{yywrap}, or if you don't use it (i.e., your scanner has no @samp{#include}-like feature), simply include a @samp{%noyywrap} statement in the scanner's source. Once this done, the scanner is portable (well, unless @emph{you} felt free to use nonportable constructs) and does not depend on any library. In this case, and in this case only, it is suggested that you use this Autoconf snippet: @example AC_PROG_LEX if test "$LEX" != flex; then LEX="$SHELL $missing_dir/missing flex" AC_SUBST(LEX_OUTPUT_ROOT, lex.yy) AC_SUBST(LEXLIB, '') fi @end example The shell script @command{missing} can be found in the Automake distribution. @end defmac @defmac AC_PROG_LN_S @maindex PROG_LN_S @ovindex LN_S If @samp{ln -s} works on the current file system (the operating system and file system support symbolic links), set output variable @code{LN_S} to @samp{ln -s}, otherwise if @samp{ln} works, set @code{LN_S} to @samp{ln}, and otherwise set to @samp{cp}. If the link is put in a directory other than the current directory, its meaning depends on whether @samp{ln} or @samp{ln -s} is used. To safely create links using @samp{$(LN_S)}, either find out which form is used and adjust the arguments, or always invoke @code{ln} in the directory where the link is to be created. In other words, it does not work to do @example $(LN_S) foo /x/bar @end example Instead, do @example (cd /x && $(LN_S) foo bar) @end example @end defmac @defmac AC_PROG_RANLIB @maindex PROG_RANLIB @ovindex RANLIB Set output variable @code{RANLIB} to @samp{ranlib} if @code{ranlib} is found, otherwise to @samp{:} (do nothing). @end defmac @defmac AC_PROG_YACC @maindex PROG_YACC @ovindex YACC If @code{bison} is found, set output variable @code{YACC} to @samp{bison -y}. Otherwise, if @code{byacc} is found, set @code{YACC} to @samp{byacc}. Otherwise set @code{YACC} to @samp{yacc}. @end defmac @node Generic Programs, , Particular Programs, Alternative Programs @subsection Generic Program and File Checks These macros are used to find programs not covered by the particular test macros. If you need to check the behavior of a program as well as find out whether it is present, you have to write your own test for it (@pxref{Writing Tests}). By default, these macros use the environment variable @code{PATH}. If you need to check for a program that might not be in the user's @code{PATH}, you can pass a modified path to use instead, like this: @example AC_PATH_PROG(INETD, inetd, /usr/libexec/inetd, $PATH:/usr/libexec:/usr/sbin:/usr/etc:etc) @end example @defmac AC_CHECK_FILE (@var{file}, @ovar{action-if-found}, @ovar{action-if-not-found}) @maindex CHECK_FILE Check whether file @var{file} exists on the native system. If it is found, execute @var{action-if-found}, otherwise do @var{action-if-not-found}, if given. @end defmac @defmac AC_CHECK_FILES (@var{files}, @ovar{action-if-found}, @ovar{action-if-not-found}) @maindex CHECK_FILES Executes @code{AC_CHECK_FILE} once for each file listed in @var{files}. Additionally, defines @samp{HAVE_@var{file}} (@pxref{Standard Symbols}) for each file found. @end defmac @defmac AC_CHECK_PROG (@var{variable}, @var{prog-to-check-for}, @var{value-if-found}, @ovar{value-if-not-found}, @ovar{path}, @ovar{reject}) @maindex CHECK_PROG Check whether program @var{prog-to-check-for} exists in @code{PATH}. If it is found, set @var{variable} to @var{value-if-found}, otherwise to @var{value-if-not-found}, if given. Always pass over @var{reject} (an absolute file name) even if it is the first found in the search path; in that case, set @var{variable} using the absolute file name of the @var{prog-to-check-for} found that is not @var{reject}. If @var{variable} was already set, do nothing. Calls @code{AC_SUBST} for @var{variable}. @end defmac @defmac AC_CHECK_PROGS (@var{variable}, @var{progs-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @maindex CHECK_PROGS Check for each program in the whitespace-separated list @var{progs-to-check-for} exists on the @code{PATH}. If it is found, set @var{variable} to the name of that program. Otherwise, continue checking the next program in the list. If none of the programs in the list are found, set @var{variable} to @var{value-if-not-found}; if @var{value-if-not-found} is not specified, the value of @var{variable} is not changed. Calls @code{AC_SUBST} for @var{variable}. @end defmac @defmac AC_CHECK_TOOL (@var{variable}, @var{prog-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @maindex CHECK_TOOL Like @code{AC_CHECK_PROG}, but first looks for @var{prog-to-check-for} with a prefix of the host type as determined by @code{AC_CANONICAL_HOST}, followed by a dash (@pxref{Canonicalizing}). For example, if the user runs @samp{configure --host=i386-gnu}, then this call: @example AC_CHECK_TOOL(RANLIB, ranlib, :) @end example @noindent sets @code{RANLIB} to @file{i386-gnu-ranlib} if that program exists in @code{PATH}, or to @samp{ranlib} if that program exists in @code{PATH}, or to @samp{:} if neither program exists. @end defmac @defmac AC_CHECK_TOOLS (@var{variable}, @var{progs-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @maindex CHECK_TOOLS Like @code{AC_CHECK_TOOL}, each of the tools in the list @var{progs-to-check-for} are checked with a prefix of the host type as determined by @code{AC_CANONICAL_HOST}, followed by a dash (@pxref{Canonicalizing}). If none of the tools can be found with a prefix, then the first one without a prefix is used. If a tool is found, set @var{variable} to the name of that program. If none of the tools in the list are found, set @var{variable} to @var{value-if-not-found}; if @var{value-if-not-found} is not specified, the value of @var{variable} is not changed. Calls @code{AC_SUBST} for @var{variable}. @end defmac @defmac AC_PATH_PROG (@var{variable}, @var{prog-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @maindex PATH_PROG Like @code{AC_CHECK_PROG}, but set @var{variable} to the entire path of @var{prog-to-check-for} if found. @end defmac @defmac AC_PATH_PROGS (@var{variable}, @var{progs-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @maindex PATH_PROGS Like @code{AC_CHECK_PROGS}, but if any of @var{progs-to-check-for} are found, set @var{variable} to the entire path of the program found. @end defmac @defmac AC_PATH_TOOL (@var{variable}, @var{prog-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @maindex PATH_TOOL Like @code{AC_PATH_PROG}, but first looks for @var{prog-to-check-for} with a prefix of the host type as determined by @code{AC_CANONICAL_HOST}, followed by a dash (@pxref{Canonicalizing}). For example, if the user runs @samp{configure --host=i386-gnu}, then this call: @example AC_PATH_TOOL(FILE, file, :, /usr/bin:$PATH) @end example @noindent sets @code{FILE} to @file{/usr/bin/i386-gnu-file}, for example, if that program is found at @file{/usr/bin} in @code{PATH}, or to @samp{/usr/bin/file}, for example, if @emph{that} program is found at @file{/usr/bin} in @code{PATH}, or to @samp{:} if neither program can be found. @end defmac @node Libraries, Library Functions, Alternative Programs, Existing Tests @section Library Files @cindex Library, checking The following macros check for the presence of certain C, C++ or Fortran 77 library archive files. @defmac AC_CHECK_LIB (@var{library}, @var{function}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{other-libraries}) @maindex CHECK_LIB Depending on the current language(@pxref{Language Choice}), try to ensure that the C, C++ or Fortran 77 function @var{function} is available by checking whether a test program can be linked with the library @var{library} to get the function. @var{library} is the base name of the library; e.g., to check for @option{-lmp}, use @samp{mp} as the @var{library} argument. @var{action-if-found} is a list of shell commands to run if the link with the library succeeds; @var{action-if-not-found} is a list of shell commands to run if the link fails. If @var{action-if-found} is not specified, the default action will prepend @option{-l@var{library}} to @code{LIBS} and define @samp{HAVE_LIB@var{library}} (in all capitals). This macro is intended to support building of @code{LIBS} in a right-to-left (least-dependent to most-dependent) fashion such that library dependencies are satisfied as a natural side-effect of consecutive tests. Some linkers are very sensitive to library ordering so the order that @code{LIBS} is generated in is important to reliable detection of libraries. If linking with @var{library} results in unresolved symbols, which would be resolved by linking with additional libraries, give those libraries as the @var{other-libraries} argument, separated by spaces: @option{-lXt -lX11}. Otherwise this macro will fail to detect that @var{library} is present, because linking the test program will always fail with unresolved symbols. The @var{other-libraries} argument should be limited to cases where it is desirable to test for the library in the presence of another (which may not already be in @code{LIBS}). @end defmac @defmac AC_SEARCH_LIBS (@var{function}, @var{search-libs}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{other-libraries}) @maindex SEARCH_LIBS Search for a library defining @var{function}, if it's not already available. This equates to calling @code{AC_TRY_LINK_FUNC} first with no libraries, then for each library listed in @var{search-libs}. Add @option{-l@var{library}} to @code{LIBS} for the first library found to contain @var{function}, and run @var{action-if-found}. If the function is not found, run @var{action-if-not-found}. If linking with @var{library} results in unresolved symbols, which would be resolved by linking with additional libraries, give those libraries as the @var{other-libraries} argument, separated by spaces: @option{-lXt -lX11}. Otherwise this macro will fail to detect that @var{function} is present, because linking the test program will always fail with unresolved symbols. @end defmac @node Library Functions, Header Files, Libraries, Existing Tests @section Library Functions The following macros check for particular C library functions. If there is no macro specifically defined to check for a function you need, and you don't need to check for any special properties of it, then you can use one of the general function check macros. @menu * Particular Functions:: Special handling to find certain functions * Generic Functions:: How to find other functions @end menu @node Particular Functions, Generic Functions, Library Functions, Library Functions @subsection Particular Function Checks @cindex Function, checking These macros check for particular C functions---whether they exist, and in some cases how they respond when given certain arguments. @defmac AC_FUNC_ALLOCA @maindex FUNC_ALLOCA @cvindex C_ALLOCA @cvindex HAVE_ALLOCA_H @ovindex ALLOCA Check how to get @code{alloca}. Tries to get a builtin version by checking for @file{alloca.h} or the predefined C preprocessor macros @code{__GNUC__} and @code{_AIX}. If this macro finds @file{alloca.h}, it defines @code{HAVE_ALLOCA_H}. If those attempts fail, it looks for the function in the standard C library. If any of those methods succeed, it defines @code{HAVE_ALLOCA}. Otherwise, it sets the output variable @code{ALLOCA} to @samp{alloca.o} and defines @code{C_ALLOCA} (so programs can periodically call @samp{alloca(0)} to garbage collect). This variable is separate from @code{LIBOBJS} so multiple programs can share the value of @code{ALLOCA} without needing to create an actual library, in case only some of them use the code in @code{LIBOBJS}. This macro does not try to get @code{alloca} from the System V R3 @file{libPW} or the System V R4 @file{libucb} because those libraries contain some incompatible functions that cause trouble. Some versions do not even contain @code{alloca} or contain a buggy version. If you still want to use their @code{alloca}, use @code{ar} to extract @file{alloca.o} from them instead of compiling @file{alloca.c}. Source files that use @code{alloca} should start with a piece of code like the following, to declare it properly. In some versions of AIX, the declaration of @code{alloca} must precede everything else except for comments and preprocessor directives. The @code{#pragma} directive is indented so that pre-@sc{ansi} C compilers will ignore it, rather than choke on it. @example @group /* AIX requires this to be the first thing in the file. */ #ifndef __GNUC__ # if HAVE_ALLOCA_H # include # else # ifdef _AIX #pragma alloca # else # ifndef alloca /* predefined by HP cc +Olibcalls */ char *alloca (); # endif # endif # endif #endif @end group @end example @end defmac @defmac AC_FUNC_CHOWN @maindex FUNC_CHOWN If the @code{chown} function is available and works (in particular it should accept @option{-1} for @code{uid} and @code{gid}), define @code{HAVE_CHOWN}. @end defmac @defmac AC_FUNC_CLOSEDIR_VOID @maindex FUNC_CLOSEDIR_VOID @cvindex CLOSEDIR_VOID If the @code{closedir} function does not return a meaningful value, define @code{CLOSEDIR_VOID}. Otherwise, callers ought to check its return value for an error indicator. @end defmac @defmac AC_FUNC_ERROR_AT_LINE @maindex FUNC_ERROR_AT_LINE If the @code{error_at_line} function is not found, require an @code{AC_LIBOBJ} replacement of @samp{error}. @end defmac @defmac AC_FUNC_FNMATCH @maindex FUNC_FNMATCH If the @code{fnmatch} function is available and works (unlike the one on SunOS 5.4), define @code{HAVE_FNMATCH}. @end defmac @defmac AC_FUNC_GETGROUPS @maindex FUNC_GETGROUPS @ovindex GETGROUPS_LIBS If the @code{getgroups} function is available and works (unlike on Ultrix 4.3 where @samp{getgroups (0, 0)} always fails), define @code{HAVE_GETGROUPS}. Set @code{GETGROUPS_LIBS} to any libraries needed to get that function. This macro runs @code{AC_TYPE_GETGROUPS}. @end defmac @defmac AC_FUNC_GETLOADAVG @maindex FUNC_GETLOADAVG @cvindex SVR4 @cvindex DGUX @cvindex UMAX @cvindex UMAX4_3 @cvindex NLIST_STRUCT @cvindex NLIST_NAME_UNION @cvindex GETLODAVG_PRIVILEGED @cvindex NEED_SETGID @cvindex C_GETLOADAVG @ovindex LIBOBJS @ovindex NEED_SETGID @ovindex KMEM_GROUP @ovindex GETLOADAVG_LIBS Check how to get the system load averages. If the system has the @code{getloadavg} function, define @code{HAVE_GETLOADAVG}, and set @code{GETLOADAVG_LIBS} to any libraries needed to get that function. Also add @code{GETLOADAVG_LIBS} to @code{LIBS}. Otherwise, require an @code{AC_LIBOBJ} replacement of @samp{getloadavg}, and possibly define several other C preprocessor macros and output variables: @enumerate @item Define @code{SVR4}, @code{DGUX}, @code{UMAX}, or @code{UMAX4_3} if on those systems. @item If @file{nlist.h} is found, define @code{NLIST_STRUCT}. @item If @samp{struct nlist} has an @samp{n_un.n_name} member, define @code{HAVE_STRUCT_NLIST_N_UN_N_NAME}. The obsolete symbol @code{NLIST_NAME_UNION} is still defined, but do not depend upon it. @item @c FIXME: I don't understand anything to this sentence :( If compiling @file{getloadavg.c} define @code{C_GETLOADAVG} and @code{LDAV_PRIVILEGED}, programs need to be installed specially on this system for @code{getloadavg} to work, and this macro defines @code{GETLOADAVG_PRIVILEGED}. @item This macro sets the output variable @code{NEED_SETGID}. The value is @samp{true} if special installation is required, @samp{false} if not. If @code{NEED_SETGID} is @samp{true}, this macro sets @code{KMEM_GROUP} to the name of the group that should own the installed program. @end enumerate @end defmac @defmac AC_FUNC_GETMNTENT @maindex FUNC_GETMNTENT @cvindex HAVE_GETMNTENT Check for @code{getmntent} in the @file{sun}, @file{seq}, and @file{gen} libraries, for Irix 4, PTX, and Unixware, respectively. Then, if @code{getmntent} is available, define @code{HAVE_GETMNTENT}. @end defmac @defmac AC_FUNC_GETPGRP @maindex FUNC_GETPGRP @cvindex GETPGRP_VOID If @code{getpgrp} takes no argument (the @sc{posix.1} version), define @code{GETPGRP_VOID}. Otherwise, it is the @sc{bsd} version, which takes a process ID as an argument. This macro does not check whether @code{getpgrp} exists at all; if you need to work in that situation, first call @code{AC_CHECK_FUNC} for @code{getpgrp}. @end defmac @defmac AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK @maindex FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK @cvindex LSTAT_FOLLOWS_SLASHED_SYMLINK If @file{link} is a symbolic link, then @code{lstat} should treat @file{link/} the same as @file{link/.}. However, many older @code{lstat} implementations incorrectly ignore trailing slashes. It is safe to assume that if @code{lstat} incorrectly ignores trailing slashes, then other symbolic-link-aware functions like @code{unlink} and @code{unlink} also incorrectly ignore trailing slashes. If @code{lstat} behaves properly, define @code{LSTAT_FOLLOWS_SLASHED_SYMLINK}, otherwise require an @code{AC_LIBOBJ} replacement of @code{lstat}. @end defmac @defmac AC_FUNC_MALLOC @maindex FUNC_MALLOC If the @code{malloc} works correctly (@samp{malloc (0)} returns a valid pointer), define @code{HAVE_MALLOC}. @end defmac @defmac AC_FUNC_MEMCMP @maindex FUNC_MEMCMP @ovindex LIBOBJS If the @code{memcmp} function is not available, or does not work on 8-bit data (like the one on SunOS 4.1.3), or fails when comparing 16 bytes or more and with at least one buffer not starting on a 4-byte boundary (such as the one on Next x86 OpenStep), require an @code{AC_LIBOBJ} replacement for @samp{memcmp}. @end defmac @defmac AC_FUNC_MKTIME @maindex FUNC_MKTIME @ovindex LIBOBJS If the @code{mktime} function is not available, or does not work correctly, require an @code{AC_LIBOBJ} replacement for @samp{mktime}. @end defmac @defmac AC_FUNC_MMAP @maindex FUNC_MMAP @cvindex HAVE_MMAP If the @code{mmap} function exists and works correctly, define @code{HAVE_MMAP}. Only checks private fixed mapping of already-mapped memory. @end defmac @defmac AC_FUNC_OBSTACK @maindex FUNC_OBSTACK @cvindex HAVE_OBSTACK @cindex obstack If the obstacks are found, define @code{HAVE_OBSTACK}, else require an @code{AC_LIBOBJ} replacement for @samp{obstack}. @end defmac @defmac AC_FUNC_SELECT_ARGTYPES @maindex FUNC_SELECT_ARGTYPES @cvindex SELECT_TYPE_ARG1 @cvindex SELECT_TYPE_ARG234 @cvindex SELECT_TYPE_ARG5 Determines the correct type to be passed to each of the @code{select} function's arguments, and defines those types in @code{SELECT_TYPE_ARG1}, @code{SELECT_TYPE_ARG234}, and @code{SELECT_TYPE_ARG5} respectively. @code{SELECT_TYPE_ARG1} defaults to @samp{int}, @code{SELECT_TYPE_ARG234} defaults to @samp{int *}, and @code{SELECT_TYPE_ARG5} defaults to @samp{struct timeval *}. @end defmac @defmac AC_FUNC_SETPGRP @maindex FUNC_SETPGRP @cvindex SETPGRP_VOID If @code{setpgrp} takes no argument (the @sc{posix.1} version), define @code{SETPGRP_VOID}. Otherwise, it is the @sc{bsd} version, which takes two process IDs as arguments. This macro does not check whether @code{setpgrp} exists at all; if you need to work in that situation, first call @code{AC_CHECK_FUNC} for @code{setpgrp}. @end defmac @defmac AC_FUNC_STAT @defmacx AC_FUNC_LSTAT @maindex FUNC_STAT @maindex FUNC_LSTAT @cvindex HAVE_STAT_EMPTY_STRING_BUG @cvindex HAVE_LSTAT_EMPTY_STRING_BUG Determine whether @code{stat} or @code{lstat} have the bug that it succeeds when given the zero-length file name argument. The @code{stat} and @code{lstat} from SunOS4.1.4 and the Hurd (as of 1998-11-01) do this. If it does, then define @code{HAVE_STAT_EMPTY_STRING_BUG} (or @code{HAVE_LSTAT_EMPTY_STRING_BUG}) and ask for an @code{AC_LIBOBJ} replacement of it. @end defmac @defmac AC_FUNC_SETVBUF_REVERSED @maindex FUNC_SETVBUF_REVERSED @cvindex SETVBUF_REVERSED If @code{setvbuf} takes the buffering type as its second argument and the buffer pointer as the third, instead of the other way around, define @code{SETVBUF_REVERSED}. @end defmac @defmac AC_FUNC_STRCOLL @maindex FUNC_STRCOLL @cvindex HAVE_STRCOLL If the @code{strcoll} function exists and works correctly, define @code{HAVE_STRCOLL}. This does a bit more than @samp{AC_CHECK_FUNCS(strcoll)}, because some systems have incorrect definitions of @code{strcoll} that should not be used. @end defmac @defmac AC_FUNC_STRTOD @maindex FUNC_STRTOD @ovindex POW_LIB If the @code{strtod} function does not exist or doesn't work correctly, ask for an @code{AC_LIBOBJ} replacement of @samp{strtod}. In this case, because @file{strtod.c} is likely to need @samp{pow}, set the output variable @code{POW_LIB} to the extra library needed. @end defmac @defmac AC_FUNC_STRERROR_R @maindex FUNC_STRERROR_R @cvindex HAVE_STRERROR_R @cvindex HAVE_WORKING_STRERROR_R If @code{strerror_r} is available, define @code{HAVE_STRERROR_R}. If its implementation correctly returns a @code{char *}, define @code{HAVE_WORKING_STRERROR_R}. On at least DEC UNIX 4.0[A-D] and HP-UX B.10.20, @code{strerror_r} returns @code{int}. Actually, this tests only whether it returns a scalar or an array, but that should be enough. This is used by the common @file{error.c}. @end defmac @defmac AC_FUNC_STRFTIME @maindex FUNC_STRFTIME @cvindex HAVE_STRFTIME Check for @code{strftime} in the @file{intl} library, for SCO @sc{unix}. Then, if @code{strftime} is available, define @code{HAVE_STRFTIME}. @end defmac @defmac AC_FUNC_UTIME_NULL @maindex FUNC_UTIME_NULL @cvindex HAVE_UTIME_NULL If @samp{utime(@var{file}, NULL)} sets @var{file}'s timestamp to the present, define @code{HAVE_UTIME_NULL}. @end defmac @defmac AC_FUNC_VFORK @maindex FUNC_VFORK @cvindex HAVE_VFORK_H @cvindex vfork If @file{vfork.h} is found, define @code{HAVE_VFORK_H}. If a working @code{vfork} is not found, define @code{vfork} to be @code{fork}. This macro checks for several known errors in implementations of @code{vfork} and considers the system to not have a working @code{vfork} if it detects any of them. It is not considered to be an implementation error if a child's invocation of @code{signal} modifies the parent's signal handler, since child processes rarely change their signal handlers. @end defmac @defmac AC_FUNC_VPRINTF @maindex FUNC_VPRINTF @cvindex HAVE_VPRINTF @cvindex HAVE_DOPRNT If @code{vprintf} is found, define @code{HAVE_VPRINTF}. Otherwise, if @code{_doprnt} is found, define @code{HAVE_DOPRNT}. (If @code{vprintf} is available, you may assume that @code{vfprintf} and @code{vsprintf} are also available.) @end defmac @defmac AC_FUNC_WAIT3 @maindex FUNC_WAIT3 @cvindex HAVE_WAIT3 If @code{wait3} is found and fills in the contents of its third argument (a @samp{struct rusage *}), which HP-UX does not do, define @code{HAVE_WAIT3}. @end defmac @node Generic Functions, , Particular Functions, Library Functions @subsection Generic Function Checks These macros are used to find functions not covered by the particular test macros. If the functions might be in libraries other than the default C library, first call @code{AC_CHECK_LIB} for those libraries. If you need to check the behavior of a function as well as find out whether it is present, you have to write your own test for it (@pxref{Writing Tests}). @defmac AC_CHECK_FUNC (@var{function}, @ovar{action-if-found}, @ovar{action-if-not-found}) @maindex CHECK_FUNC If C function @var{function} is available, run shell commands @var{action-if-found}, otherwise @var{action-if-not-found}. If you just want to define a symbol if the function is available, consider using @code{AC_CHECK_FUNCS} instead. This macro checks for functions with C linkage even when @code{AC_LANG(C++)} has been called, since C++ is more standardized than C is. (@pxref{Language Choice}, for more information about selecting the language for checks.) @end defmac @defmac AC_CHECK_FUNCS (@var{function}@dots{}, @ovar{action-if-found}, @ovar{action-if-not-found}) @maindex CHECK_FUNCS @cvindex HAVE_@var{function} For each given @var{function} in the whitespace-separated argument list that is available, define @code{HAVE_@var{function}} (in all capitals). If @var{action-if-found} is given, it is additional shell code to execute when one of the functions is found. You can give it a value of @samp{break} to break out of the loop on the first match. If @var{action-if-not-found} is given, it is executed when one of the functions is not found. @end defmac Autoconf follows a philosophy that was formed throughout the years by the people who fought for portability: isolate the portability issues in specific files, and program as if you were in a @sc{posix} environment. Some functions cannot be repaired or are completely missing; your package must be ready to replace them. Use the two following macros to specify the function that might be replaced, and use the third one to check and replace a function if needed. @defmac AC_LIBOBJ (@var{function}) @maindex LIBOBJ @ovindex LIBOBJS Specify that @samp{@var{function}.c} must be included in the executables to replace a missing or broken implementation of @var{function}. Technically it adds @samp{@var{function}.$ac_objext} to the output variable @code{LIBOBJS}, nevertheless you must not directly change @code{LIBOBJS} since this is not traceable. @end defmac @defmac AC_LIBOBJ_DECL (@var{function}) @maindex LIBOBJ_DECL @ovindex LIBOBJS Specify that @samp{@var{function}.c} might be needed to compile the project. You must use this macro when you are calling @code{AC_LIBOBJ} with a shell variable, since shell variables cannot be traced statically. @var{function} must be a literal. For instance you might need to: @example AC_LIBOBJ_DECL(foo) AC_LIBOBJ_DECL(bar) AC_LIBOBJ($foo_or_bar) @end example @noindent nevertheless, there is always a means to avoid this, and you are encouraged to always uses literals with @code{AC_LIBOBJ}. Conversely, if you need to know what are the files that might be needed by a @file{configure.in}, you should trace @code{AC_LIBOBJ_DECL}. @end defmac @defmac AC_REPLACE_FUNCS (@var{function}@dots{}) @maindex REPLACE_FUNCS @ovindex LIBOBJS Like calling @code{AC_CHECK_FUNCS} using @samp{AC_LIBOBJ(@var{function})} as @var{action-if-not-found}. You can declare a function for which your replacement version is used by enclosing the prototype in @samp{#if !HAVE_@var{function}}. If the system has the function, it probably declares it in a header file you should be including, so you shouldn't redeclare it, lest your declaration conflict. @end defmac @node Header Files, Declarations, Library Functions, Existing Tests @section Header Files @cindex Header, checking The following macros check for the presence of certain C header files. If there is no macro specifically defined to check for a header file you need, and you don't need to check for any special properties of it, then you can use one of the general header file check macros. @menu * Particular Headers:: Special handling to find certain headers * Generic Headers:: How to find other headers @end menu @node Particular Headers, Generic Headers, Header Files, Header Files @subsection Particular Header Checks These macros check for particular system header files---whether they exist, and in some cases whether they declare certain symbols. @defmac AC_HEADER_DIRENT @maindex HEADER_DIRENT @cvindex HAVE_DIRENT_H @cvindex HAVE_NDIR_H @cvindex HAVE_SYS_DIR_H @cvindex HAVE_SYS_NDIR_H Check for the following header files, and for the first one that is found and defines @samp{DIR}, define the listed C preprocessor macro: @multitable {@file{sys/ndir.h}} {@code{HAVE_SYS_NDIR_H}} @item @file{dirent.h} @tab @code{HAVE_DIRENT_H} @item @file{sys/ndir.h} @tab @code{HAVE_SYS_NDIR_H} @item @file{sys/dir.h} @tab @code{HAVE_SYS_DIR_H} @item @file{ndir.h} @tab @code{HAVE_NDIR_H} @end multitable The directory library declarations in the source code should look something like the following: @example @group #if HAVE_DIRENT_H # include # define NAMLEN(dirent) strlen((dirent)->d_name) #else # define dirent direct # define NAMLEN(dirent) (dirent)->d_namlen # if HAVE_SYS_NDIR_H # include # endif # if HAVE_SYS_DIR_H # include # endif # if HAVE_NDIR_H # include # endif #endif @end group @end example Using the above declarations, the program would declare variables to be type @code{struct dirent}, not @code{struct direct}, and would access the length of a directory entry name by passing a pointer to a @code{struct dirent} to the @code{NAMLEN} macro. This macro also checks for the SCO Xenix @file{dir} and @file{x} libraries. @end defmac @defmac AC_HEADER_MAJOR @maindex HEADER_MAJOR @cvindex MAJOR_IN_MKDEV @cvindex MAJOR_IN_SYSMACROS If @file{sys/types.h} does not define @code{major}, @code{minor}, and @code{makedev}, but @file{sys/mkdev.h} does, define @code{MAJOR_IN_MKDEV}; otherwise, if @file{sys/sysmacros.h} does, define @code{MAJOR_IN_SYSMACROS}. @end defmac @defmac AC_HEADER_STAT @maindex HEADER_STAT @maindex STAT_MACROS_BROKEN If the macros @code{S_ISDIR}, @code{S_ISREG} et al. defined in @file{sys/stat.h} do not work properly (returning false positives), define @code{STAT_MACROS_BROKEN}. This is the case on Tektronix UTekV, Amdahl UTS and Motorola System V/88. @end defmac @defmac AC_HEADER_STDC @maindex HEADER_STDC @cvindex STDC_HEADERS Define @code{STDC_HEADERS} if the system has @sc{ansi} C header files. Specifically, this macro checks for @file{stdlib.h}, @file{stdarg.h}, @file{string.h}, and @file{float.h}; if the system has those, it probably has the rest of the @sc{ansi} C header files. This macro also checks whether @file{string.h} declares @code{memchr} (and thus presumably the other @code{mem} functions), whether @file{stdlib.h} declare @code{free} (and thus presumably @code{malloc} and other related functions), and whether the @file{ctype.h} macros work on characters with the high bit set, as @sc{ansi} C requires. Use @code{STDC_HEADERS} instead of @code{__STDC__} to determine whether the system has @sc{ansi}-compliant header files (and probably C library functions) because many systems that have GCC do not have @sc{ansi} C header files. On systems without @sc{ansi} C headers, there is so much variation that it is probably easier to declare the functions you use than to figure out exactly what the system header files declare. Some systems contain a mix of functions @sc{ansi} and @sc{bsd}; some are mostly @sc{ansi} but lack @samp{memmove}; some define the @sc{bsd} functions as macros in @file{string.h} or @file{strings.h}; some have only the @sc{bsd} functions but @file{string.h}; some declare the memory functions in @file{memory.h}, some in @file{string.h}; etc. It is probably sufficient to check for one string function and one memory function; if the library has the @sc{ansi} versions of those then it probably has most of the others. If you put the following in @file{configure.in}: @example AC_HEADER_STDC AC_CHECK_FUNCS(strchr memcpy) @end example @noindent then, in your code, you can put declarations like this: @example @group #if STDC_HEADERS # include #else # if !HAVE_STRCHR # define strchr index # define strrchr rindex # endif char *strchr (), *strrchr (); # if !HAVE_MEMCPY # define memcpy(d, s, n) bcopy ((s), (d), (n)) # define memmove(d, s, n) bcopy ((s), (d), (n)) # endif #endif @end group @end example @noindent If you use a function like @code{memchr}, @code{memset}, @code{strtok}, or @code{strspn}, which have no @sc{bsd} equivalent, then macros won't suffice; you must provide an implementation of each function. An easy way to incorporate your implementations only when needed (since the ones in system C libraries may be hand optimized) is to, taking @code{memchr} for example, put it in @file{memchr.c} and use @samp{AC_REPLACE_FUNCS(memchr)}. @end defmac @defmac AC_HEADER_SYS_WAIT @maindex HEADER_SYS_WAIT @cvindex HAVE_SYS_WAIT_H If @file{sys/wait.h} exists and is compatible with @sc{posix.1}, define @code{HAVE_SYS_WAIT_H}. Incompatibility can occur if @file{sys/wait.h} does not exist, or if it uses the old @sc{bsd} @code{union wait} instead of @code{int} to store a status value. If @file{sys/wait.h} is not @sc{posix.1} compatible, then instead of including it, define the @sc{posix.1} macros with their usual interpretations. Here is an example: @example @group #include #if HAVE_SYS_WAIT_H # include #endif #ifndef WEXITSTATUS # define WEXITSTATUS(stat_val) ((unsigned)(stat_val) >> 8) #endif #ifndef WIFEXITED # define WIFEXITED(stat_val) (((stat_val) & 255) == 0) #endif @end group @end example @end defmac @cvindex _POSIX_VERSION @code{_POSIX_VERSION} is defined when @file{unistd.h} is included on @sc{posix.1} systems. If there is no @file{unistd.h}, it is definitely not a @sc{posix.1} system. However, some non-@sc{posix.1} systems do have @file{unistd.h}. The way to check if the system supports @sc{posix.1} is: @example @group #if HAVE_UNISTD_H # include # include #endif #ifdef _POSIX_VERSION /* Code for POSIX.1 systems. */ #endif @end group @end example @defmac AC_HEADER_TIME @maindex HEADER_TIME @cvindex TIME_WITH_SYS_TIME If a program may include both @file{time.h} and @file{sys/time.h}, define @code{TIME_WITH_SYS_TIME}. On some older systems, @file{sys/time.h} includes @file{time.h}, but @file{time.h} is not protected against multiple inclusion, so programs should not explicitly include both files. This macro is useful in programs that use, for example, @code{struct timeval} or @code{struct timezone} as well as @code{struct tm}. It is best used in conjunction with @code{HAVE_SYS_TIME_H}, which can be checked for using @code{AC_CHECK_HEADERS(sys/time.h)}. @example @group #if TIME_WITH_SYS_TIME # include # include #else # if HAVE_SYS_TIME_H # include # else # include # endif #endif @end group @end example @end defmac @defmac AC_HEADER_TIOCGWINSZ @maindex HEADER_TIOCGWINSZ @cvindex GWINSZ_IN_SYS_IOCTL @c FIXME: I need clarifications from Jim. If the use of @code{TIOCGWINSZ} requires @file{}, then define @code{GWINSZ_IN_SYS_IOCTL}. Otherwise @code{TIOCGWINSZ} can be found in @file{}. Use: @example @group #if HAVE_TERMIOS_H # include #endif #if GWINSZ_IN_SYS_IOCTL # include #endif @end group @end example @end defmac @node Generic Headers, , Particular Headers, Header Files @subsection Generic Header Checks These macros are used to find system header files not covered by the particular test macros. If you need to check the contents of a header as well as find out whether it is present, you have to write your own test for it (@pxref{Writing Tests}). @defmac AC_CHECK_HEADER (@var{header-file}, @ovar{action-if-found}, @ovar{action-if-not-found}) @maindex CHECK_HEADER If the system header file @var{header-file} exists, execute shell commands @var{action-if-found}, otherwise execute @var{action-if-not-found}. If you just want to define a symbol if the header file is available, consider using @code{AC_CHECK_HEADERS} instead. @end defmac @defmac AC_CHECK_HEADERS (@var{header-file}@dots{}, @ovar{action-if-found}, @ovar{action-if-not-found}) @maindex CHECK_HEADERS @cvindex HAVE_@var{header} For each given system header file @var{header-file} in the whitespace-separated argument list that exists, define @code{HAVE_@var{header-file}} (in all capitals). If @var{action-if-found} is given, it is additional shell code to execute when one of the header files is found. You can give it a value of @samp{break} to break out of the loop on the first match. If @var{action-if-not-found} is given, it is executed when one of the header files is not found. @end defmac @node Declarations, Structures, Header Files, Existing Tests @section Declarations @cindex Declaration, checking The following macros check for the declaration of variables and functions. If there is no macro specifically defined to check for a symbol you need, then you can use the general macro (@pxref{Generic Declarations}) or, for more complex tests, you may use @code{AC_TRY_COMPILE} (@pxref{Examining Syntax}). @menu * Particular Declarations:: Macros to check for certain declarations * Generic Declarations:: How to find other declarations @end menu @node Particular Declarations, Generic Declarations, Declarations, Declarations @subsection Particular Declaration Checks The following macros check for certain declarations. @defmac AC_DECL_SYS_SIGLIST @maindex DECL_SYS_SIGLIST @cvindex SYS_SIGLIST_DECLARED Define @code{SYS_SIGLIST_DECLARED} if the variable @code{sys_siglist} is declared in a system header file, either @file{signal.h} or @file{unistd.h}. @end defmac @node Generic Declarations, , Particular Declarations, Declarations @subsection Generic Declaration Checks These macros are used to find declarations not covered by the particular test macros. @defmac AC_CHECK_DECL (@var{symbol}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{includes}) @maindex CHECK_DECL If the declaration of @var{symbol} (a function or a variable) is needed because it is not declared in @var{includes}, run the shell commands @var{action-if-not-found}, otherwise @var{action-if-found}. If no @var{includes} are specified, the default includes are used (@pxref{Default Includes}). This macro actually tests whether it is valid to use @var{symbol} as an r-value, not if it is really declared, because it is much safer to avoid introducing extra declarations when not needed. @end defmac @defmac AC_CHECK_DECLS (@var{symbols}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{includes}) @maindex CHECK_DECLS @cvindex HAVE_DECL_@var{symbol} For each of the @var{symbols} (comma separated list), define @code{HAVE_DECL_@var{symbol}} (in all capitals) to @samp{1} if @var{symbol} is declared, otherwise to @samp{0}. If @var{action-if-not-found} is given, it is additional shell code to execute when one of the function declarations is needed, otherwise @var{action-if-found} is executed. This macro uses an m4 list as first argument: @example AC_CHECK_DECLS(strdup) AC_CHECK_DECLS([strlen]) AC_CHECK_DECLS([malloc, realloc, calloc, free]) @end example Unlike the other @samp{AC_CHECK_*S} macros, when a @var{symbol} is not declared, @code{HAVE_DECL_@var{symbol}} is defined to @samp{0} instead of leaving @code{HAVE_DECL_@var{symbol}} undeclared. When you are @emph{sure} that the check was performed, use @code{HAVE_DECL_@var{symbol}} just like any other result of Autoconf: @example #if !HAVE_DECL_SYMBOL extern char *symbol; #endif @end example @noindent But if the test may have not been performed, because it is safer @emph{not} to declare a symbol than to use a declaration that conflicts with the system's one, you should use: @example #if defined HAVE_DECL_MALLOC && !HAVE_DECL_MALLOC char *malloc (size_t *s); #endif @end example @noindent You fall into the second category only in extreme situations: either your files may be used without being configured, or they are used during the configuration. In most cases the traditional approach is enough. @end defmac @node Structures, Types, Declarations, Existing Tests @section Structures @cindex Structure, checking The following macros check for the presence of certain members in C structures. If there is no macro specifically defined to check for a member you need, then you can use the general structure member macro (@pxref{Generic Structures}) or, for more complex tests, you may use @code{AC_TRY_COMPILE} (@pxref{Examining Syntax}). @menu * Particular Structures:: Macros to check for certain structure members * Generic Structures:: How to find other structure members @end menu @node Particular Structures, Generic Structures, Structures, Structures @subsection Particular Structure Checks The following macros check for certain structures or structure members. @defmac AC_STRUCT_ST_BLKSIZE @maindex STRUCT_ST_BLKSIZE @cvindex HAVE_STRUCT_STAT_ST_BLKSIZE @cvindex HAVE_ST_BLKSIZE If @code{struct stat} contains an @code{st_blksize} member, define @code{HAVE_STRUCT_STAT_ST_BLKSIZE}. The former name, @code{HAVE_ST_BLKSIZE} is to be avoided, as its support will cease in the future. This macro is obsoleted, and should be replaced by @example AC_CHECK_MEMBERS((struct stat.st_blksize)) @end example @end defmac @defmac AC_STRUCT_ST_BLOCKS @maindex STRUCT_ST_BLOCKS @cvindex HAVE_STRUCT_STAT_ST_BLOCKS @cvindex HAVE_ST_BLOCKS @ovindex LIBOBJS If @code{struct stat} contains an @code{st_blocks} member, define @code{HAVE_STRUCT STAT_ST_BLOCKS}. Otherwise, require an @code{AC_LIBOBJ} replacement of @samp{fileblocks}. The former name, @code{HAVE_ST_BLOCKS} is to be avoided, as its support will cease in the future. @end defmac @defmac AC_STRUCT_ST_RDEV @maindex STRUCT_ST_RDEV @cvindex HAVE_ST_RDEV @cvindex HAVE_STRUCT_STAT_ST_RDEV If @code{struct stat} contains an @code{st_rdev} member, define @code{HAVE_STRUCT_STAT_ST_RDEV}. The former name, @code{HAVE_ST_RDEV} is to be avoided, as its support will cease in the future. This macro is obsoleted, and should be replaced by @example AC_CHECK_MEMBERS((struct stat.st_rdev)) @end example @end defmac @defmac AC_STRUCT_TM @maindex STRUCT_TM @cvindex TM_IN_SYS_TIME If @file{time.h} does not define @code{struct tm}, define @code{TM_IN_SYS_TIME}, which means that including @file{sys/time.h} had better define @code{struct tm}. @end defmac @defmac AC_STRUCT_TIMEZONE @maindex STRUCT_TIMEZONE @cvindex HAVE_TM_ZONE @cvindex HAVE_TZNAME Figure out how to get the current timezone. If @code{struct tm} has a @code{tm_zone} member, define @code{HAVE_STRUCT_TM_TM_ZONE} (and the obsoleted @code{HAVE_TM_ZONE}). Otherwise, if the external array @code{tzname} is found, define @code{HAVE_TZNAME}. @end defmac @node Generic Structures, , Particular Structures, Structures @subsection Generic Structure Checks These macros are used to find structure members not covered by the particular test macros. @defmac AC_CHECK_MEMBER (@var{aggregate}.@var{member}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{includes}) @maindex CHECK_MEMBER Check whether @var{member} is a member of the aggregate @var{aggregate}. If no @var{includes} are specified, the default includes are used (@pxref{Default Includes}). @example AC_CHECK_MEMBER(struct passwd.pw_gecos,, [AC_MSG_ERROR([We need `struct passwd.pw_gecos'!])], [#include ]) @end example You can use this macro for sub members: @example AC_CHECK_MEMBER(struct top.middle.bot) @end example @end defmac @defmac AC_CHECK_MEMBERS (@var{members}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{includes}) @maindex CHECK_MEMBERS Check for the existence of each @samp{@var{aggregate}.@var{member}} of @var{members} using the previous macro. When @var{member} belong to @var{aggregate}, define @code{HAVE_@var{aggregate}_@var{member}} (in all capitals, with spaces and dot replaced by underscore). This macro uses m4 lists: @example AC_CHECK_MEMBERS([struct stat.st_rdev, struct stat.st_blksize]) @end example @end defmac @node Types, Compilers and Preprocessors, Structures, Existing Tests @section Types The following macros check for C types, either builtin or typedefs. If there is no macro specifically defined to check for a type you need, and you don't need to check for any special properties of it, then you can use a general type check macro. @menu * Particular Types:: Special handling to find certain types * Generic Types:: How to find other types @end menu @node Particular Types, Generic Types, Types, Types @subsection Particular Type Checks These macros check for particular C types in @file{sys/types.h}, @file{stdlib.h} and others, if they exist. @defmac AC_TYPE_GETGROUPS @maindex TYPE_GETGROUPS @cvindex GETGROUPS_T Define @code{GETGROUPS_T} to be whichever of @code{gid_t} or @code{int} is the base type of the array argument to @code{getgroups}. @end defmac @defmac AC_TYPE_MODE_T @maindex TYPE_MODE_T @cvindex mode_t Equivalent to @samp{AC_CHECK_TYPE(mode_t, int)}. @end defmac @defmac AC_TYPE_OFF_T @maindex TYPE_OFF_T @cvindex off_t Equivalent to @samp{AC_CHECK_TYPE(off_t, long)}. @end defmac @defmac AC_TYPE_PID_T @maindex TYPE_PID_T @cvindex pid_t Equivalent to @samp{AC_CHECK_TYPE(pid_t, int)}. @end defmac @defmac AC_TYPE_SIGNAL @maindex TYPE_SIGNAL @cvindex RETSIGTYPE If @file{signal.h} declares @code{signal} as returning a pointer to a function returning @code{void}, define @code{RETSIGTYPE} to be @code{void}; otherwise, define it to be @code{int}. Define signal handlers as returning type @code{RETSIGTYPE}: @example @group RETSIGTYPE hup_handler () @{ @dots{} @} @end group @end example @end defmac @defmac AC_TYPE_SIZE_T @maindex TYPE_SIZE_T @cvindex size_t Equivalent to @samp{AC_CHECK_TYPE(size_t, unsigned)}. @end defmac @defmac AC_TYPE_UID_T @maindex TYPE_UID_T @cvindex uid_t @cvindex gid_t If @code{uid_t} is not defined, define @code{uid_t} to be @code{int} and @code{gid_t} to be @code{int}. @end defmac @node Generic Types, , Particular Types, Types @subsection Generic Type Checks These macros are used to check for types not covered by the particular test macros. @defmac AC_CHECK_TYPE (@var{type}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{includes}) @maindex CHECK_TYPE Check whether @var{type} is defined. It may be a compiler builtin type or defined by the @ovar{includes} (@pxref{Default Includes}). @end defmac @defmac AC_CHECK_TYPES (@var{types}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{includes}) @maindex CHECK_TYPES For each @var{type} of the @var{types} that is defined, define @code{HAVE_@var{type}} (in all capitals). If no @var{includes} are specified, the default includes are used (@pxref{Default Includes}). If @var{action-if-found} is given, it is additional shell code to execute when one of the types is found. If @var{action-if-not-found} is given, it is executed when one of the types is not found. This macro uses m4 lists: @example AC_CHECK_TYPES(ptrdiff_t) AC_CHECK_TYPES([unsigned long long, uintmax_t]) @end example @end defmac Autoconf, up to 2.13, used to provide to another version of @code{AC_CHECK_TYPE}, broken by design. In order to keep backward compatibility, a simple heuristics, quite safe but not totally, is implemented. In case of doubt, read the documentation of the former @code{AC_CHECK_TYPE}, see @ref{Obsolete Macros}. @node Compilers and Preprocessors, C Compiler Characteristics, Types, Existing Tests @section Compilers and Preprocessors @ovindex EXEEXT All the tests for compilers (@code{AC_PROG_CC}, @code{AC_PROG_CXX}, @code{AC_PROG_F77}) define the output variable @code{EXEEXT} based on the output of the compiler, typically to the empty string if Unix and @samp{.exe} if Win32 or OS/2. @ovindex CYGWIN @ovindex EMXOS2 @ovindex MINGW32 They also set the shell variable @code{CYGWIN} to @samp{yes} if run in the Cygwin environment, @code{EMXOS2} to @samp{yes} if in the EMX environment on OS/2, and @code{MINGW32} to @samp{yes} with the MingW32 compiler. @ovindex OBJEXT Finally, they define the output variable @code{OBJEXT} based on the output of the compiler, after .c files have been excluded, typically to @samp{o} if Unix, @samp{obj} if Win32. If the compiler being used does not produce executables, they fail. If the executables can't be run, and cross-compilation is not enabled, they fail too. @xref{Manual Configuration}, for more on support for cross compiling. @defmac AC_PROG_CC (@ovar{compiler-search-list}) @maindex PROG_CC @ovindex CC @ovindex CFLAGS Determine a C compiler to use. If @code{CC} is not already set in the environment, check for @code{gcc} and @code{cc}, then for other C compilers. Set output variable @code{CC} to the name of the compiler found. This macro may, however, be invoked with an optional first argument which, if specified, must be a space separated list of C compilers to search for. This just gives the user an opportunity to specify an alternative search list for the C compiler. For example, if you didn't like the default order, then you could invoke @code{AC_PROG_CC} like this: @example AC_PROG_CC(cl egcs gcc cc) @end example If using the @sc{gnu} C compiler, set shell variable @code{GCC} to @samp{yes}. If output variable @code{CFLAGS} was not already set, set it to @option{-g -O2} for the @sc{gnu} C compiler (@option{-O2} on systems where GCC does not accept @option{-g}), or @option{-g} for other compilers. @end defmac @defmac AC_PROG_CC_C_O @maindex PROG_CC_C_O @cvindex NO_MINUS_C_MINUS_O If the C compiler does not accept the @option{-c} and @option{-o} options simultaneously, define @code{NO_MINUS_C_MINUS_O}. This macro actually tests both the compiler found by @code{AC_PROG_CC}, and, if different, the first @code{cc} in the path. The test fails if one fails. This macro was created for @sc{gnu} Make to choose the default C compilation rule. @end defmac @defmac AC_PROG_CC_STDC @maindex PROG_CC_STDC @ovindex CC If the C compiler is not in @sc{ansi} C mode by default, try to add an option to output variable @code{CC} to make it so. This macro tries various options that select @sc{ansi} C on some system or another. It considers the compiler to be in @sc{ansi} C mode if it handles function prototypes correctly. If you use this macro, you should check after calling it whether the C compiler has been set to accept @sc{ansi} C; if not, the shell variable @code{ac_cv_prog_cc_stdc} is set to @samp{no}. If you wrote your source code in @sc{ansi} C, you can make an un-@sc{ansi}fied copy of it by using the program @code{ansi2knr}, which comes with Automake. @end defmac @defmac AC_PROG_CPP @maindex PROG_CPP @ovindex CPP Set output variable @code{CPP} to a command that runs the C preprocessor. If @samp{$CC -E} doesn't work, @file{/lib/cpp} is used. It is only portable to run @code{CPP} on files with a @file{.c} extension. If the current language is C (@pxref{Language Choice}), many of the specific test macros use the value of @code{CPP} indirectly by calling @code{AC_TRY_CPP}, @code{AC_CHECK_HEADER}, @code{AC_EGREP_HEADER}, or @code{AC_EGREP_CPP}. Some preprocessors don't indicate missing include files by the error status. For such preprocessors an internal variable is set that causes other macros to check the standard error from the preprocessor and consider the test failed if any warnings have been reported. @end defmac @defmac AC_PROG_CXX (@ovar{compiler-search-list}) @maindex PROG_CXX @ovindex CXX @ovindex CXXFLAGS Determine a C++ compiler to use. Check if the environment variable @code{CXX} or @code{CCC} (in that order) is set; if so, then set output variable @code{CXX} to its value. Otherwise, if the macro is invoked without an argument, then search for a C++ compiler under the likely names (first @code{g++} and @code{c++} then other names). If none of those checks succeed, then as a last resort set @code{CXX} to @code{gcc}. This macro may, however, be invoked with an optional first argument which, if specified, must be a space separated list of C++ compilers to search for. This just gives the user an opportunity to specify an alternative search list for the C++ compiler. For example, if you didn't like the default order, then you could invoke @code{AC_PROG_CXX} like this: @example AC_PROG_CXX(cl KCC CC cxx cc++ xlC aCC c++ g++ egcs gcc) @end example If using the @sc{gnu} C++ compiler, set shell variable @code{GXX} to @samp{yes}. If output variable @code{CXXFLAGS} was not already set, set it to @option{-g -O2} for the @sc{gnu} C++ compiler (@option{-O2} on systems where G++ does not accept @option{-g}), or @option{-g} for other compilers. @end defmac @defmac AC_PROG_CXXCPP @maindex PROG_CXXCPP @ovindex CXXCPP Set output variable @code{CXXCPP} to a command that runs the C++ preprocessor. If @samp{$CXX -E} doesn't work, @file{/lib/cpp} is used. It is only portable to run @code{CXXCPP} on files with a @file{.c}, @file{.C}, or @file{.cc} extension. If the current language is C++ (@pxref{Language Choice}), many of the specific test macros use the value of @code{CXXCPP} indirectly by calling @code{AC_TRY_CPP}, @code{AC_CHECK_HEADER}, @code{AC_EGREP_HEADER}, or @code{AC_EGREP_CPP}. Some preprocessors don't indicate missing include files by the error status. For such preprocessors an internal variable is set that causes other macros to check the standard error from the preprocessor and consider the test failed if any warnings have been reported. However, it is not known whether such broken preprocessors exist for C++. @end defmac @defmac AC_PROG_F77 (@ovar{compiler-search-list}) @maindex PROG_FORTRAN @ovindex F77 @ovindex FFLAGS Determine a Fortran 77 compiler to use. If @code{F77} is not already set in the environment, then check for @code{g77} and @code{f77}, and then some other names. Set the output variable @code{F77} to the name of the compiler found. This macro may, however, be invoked with an optional first argument which, if specified, must be a space separated list of Fortran 77 compilers to search for. This just gives the user an opportunity to specify an alternative search list for the Fortran 77 compiler. For example, if you didn't like the default order, then you could invoke @code{AC_PROG_F77} like this: @example AC_PROG_F77(fl32 f77 fort77 xlf cf77 g77 f90 xlf90) @end example If using @code{g77} (the @sc{gnu} Fortran 77 compiler), then @code{AC_PROG_F77} will set the shell variable @code{G77} to @samp{yes}. If the output variable @code{FFLAGS} was not already set in the environment, then set it to @option{-g -02} for @code{g77} (or @option{-O2} where @code{g77} does not accept @option{-g}). Otherwise, set @code{FFLAGS} to @option{-g} for all other Fortran 77 compilers. @end defmac @defmac AC_PROG_F77_C_O @maindex PROG_F77_C_O @cvindex F77_NO_MINUS_C_MINUS_O Test if the Fortran 77 compiler accepts the options @option{-c} and @option{-o} simultaneously, and define @code{F77_NO_MINUS_C_MINUS_O} if it does not. @end defmac @defmac AC_PROG_GCC_TRADITIONAL @maindex PROG_GCC_TRADITIONAL @ovindex CC Add @option{-traditional} to output variable @code{CC} if using the @sc{gnu} C compiler and @code{ioctl} does not work properly without @option{-traditional}. That usually happens when the fixed header files have not been installed on an old system. Since recent versions of the @sc{gnu} C compiler fix the header files automatically when installed, this is becoming a less prevalent problem. @end defmac @node C Compiler Characteristics, Fortran 77 Compiler Characteristics, Compilers and Preprocessors, Existing Tests @section C Compiler Characteristics The following macros check for C compiler or machine architecture features. To check for characteristics not listed here, use @code{AC_TRY_COMPILE} (@pxref{Examining Syntax}) or @code{AC_TRY_RUN} (@pxref{Run Time}) @defmac AC_C_BIGENDIAN @maindex C_BIGENDIAN @cvindex WORDS_BIGENDIAN @cindex Endianness If words are stored with the most significant byte first (like Motorola and SPARC, but not Intel and VAX, CPUs), define @code{WORDS_BIGENDIAN}. @end defmac @defmac AC_C_CONST @maindex C_CONST @cvindex const If the C compiler does not fully support the @sc{ansi} C qualifier @code{const}, define @code{const} to be empty. Some C compilers that do not define @code{__STDC__} do support @code{const}; some compilers that define @code{__STDC__} do not completely support @code{const}. Programs can simply use @code{const} as if every C compiler supported it; for those that don't, the @file{Makefile} or configuration header file will define it as empty. Occasionally installers use a C++ compiler to compile C code, typically because they lack a C compiler. This causes problems with @code{const}, because C and C++ treat @code{const} differently. For example: @example const int foo; @end example @noindent is valid in C but not in C++. These differences unfortunately cannot be papered over by defining @code{const} to be empty. If @code{autoconf} detects this situation, it leaves @code{const} alone, as this generally yields better results in practice. However, using a C++ compiler to compile C code is not recommended or supported, and installers who run into trouble in this area should get a C compiler like GCC to compile their C code. @end defmac @defmac AC_C_VOLATILE @maindex C_VOLATILE @cvindex volatile If the C compiler does not understand the keyword @code{volatile}, define @code{volatile} to be empty. Programs can simply use @code{volatile} as if every C compiler supported it; for those that do not, the @file{Makefile} or configuration header will define it as empty. If the correctness of your program depends on the semantics of @code{volatile}, simply defining it to be empty does, in a sense, break your code. However, given that the compiler does not support @code{volatile}, you are at its mercy anyway. At least your program will compile, when it wouldn't before. In general, the @code{volatile} keyword is a feature of @sc{ansi} C, so you might expect that @code{volatile} is available only when @code{__STDC__} is defined. However, Ultrix 4.3's native compiler does support volatile, but does not defined @code{__STDC__}. @end defmac @defmac AC_C_INLINE @maindex C_INLINE @cvindex inline If the C compiler supports the keyword @code{inline}, do nothing. Otherwise define @code{inline} to @code{__inline__} or @code{__inline} if it accepts one of those, otherwise define @code{inline} to be empty. @end defmac @defmac AC_C_CHAR_UNSIGNED @maindex C_CHAR_UNSIGNED @cvindex __CHAR_UNSIGNED__ If the C type @code{char} is unsigned, define @code{__CHAR_UNSIGNED__}, unless the C compiler predefines it. @end defmac @defmac AC_C_LONG_DOUBLE @maindex C_LONG_DOUBLE @cvindex HAVE_LONG_DOUBLE If the C compiler supports the @code{long double} type, define @code{HAVE_LONG_DOUBLE}. Some C compilers that do not define @code{__STDC__} do support the @code{long double} type; some compilers that define @code{__STDC__} do not support @code{long double}. @end defmac @defmac AC_C_STRINGIZE @maindex C_STRINGIZE @cvindex HAVE_STRINGIZE If the C preprocessor supports the stringizing operator, define @code{HAVE_STRINGIZE}. The stringizing operator is @samp{#} and is found in macros such as this: @example #define x(y) #y @end example @end defmac @defmac AC_C_PROTOTYPES @maindex C_PROTOTYPES @cvindex PROTOTYPES @cvindex PARAMS Check to see if function prototypes are understood by the compiler. If so, define @samp{PROTOTYPES}. In the case the compiler does not handle prototypes, you should use @code{ansi2knr}, which comes with the Automake distribution, to unprotoize function definitions. For function prototypes, you should first define @code{PARAMS}: @example #ifndef PARAMS # if PROTOTYPES # define PARAMS(protos) protos # else /* no PROTOTYPES */ # define PARAMS(protos) () # endif /* no PROTOTYPES */ #endif @end example @noindent then use it this way: @example size_t my_strlen PARAMS ((const char *)); @end example @end defmac @c FIXME: What the heck is this macro doing here? Move it out of @c the way, in its proper section!!! @defmac AC_CHECK_SIZEOF (@var{type}, @ovar{unused}, @ovar{includes}) @maindex CHECK_SIZEOF Define @code{SIZEOF_@var{type}} (@pxref{Standard Symbols}) to be the size in bytes of @var{type}. If @samp{type} is unknown, it gets a size of 0. If no @var{includes} are specified, the default includes are used (@pxref{Default Includes}). If you provide @var{include}, make sure to include @file{stdio.h} which is required for this macro to run. This macro now works even when cross-compiling. The @var{unused} argument was used when cross-compiling. For example, the call @example AC_CHECK_SIZEOF(int *) @end example @noindent defines @code{SIZEOF_INT_P} to be 8 on DEC Alpha AXP systems. @end defmac @node Fortran 77 Compiler Characteristics, System Services, C Compiler Characteristics, Existing Tests @section Fortran 77 Compiler Characteristics The following macros check for Fortran 77 compiler characteristics. To check for characteristics not listed here, use @code{AC_TRY_COMPILE} (@pxref{Examining Syntax}) or @code{AC_TRY_RUN} (@pxref{Run Time}), making sure to first set the current language to Fortran 77 @code{AC_LANG_FORTRAN77} (@pxref{Language Choice}). @defmac AC_F77_LIBRARY_LDFLAGS @maindex F77_LIBRARY_LDFLAGS @ovindex FLIBS Determine the linker flags (e.g. @option{-L} and @option{-l}) for the @dfn{Fortran 77 intrinsic and run-time libraries} that are required to successfully link a Fortran 77 program or shared library. The output variable @code{FLIBS} is set to these flags. This macro is intended to be used in those situations when it is necessary to mix, e.g. C++ and Fortran 77 source code into a single program or shared library (@pxref{Mixing Fortran 77 With C and C++,,, automake, GNU Automake}). For example, if object files from a C++ and Fortran 77 compiler must be linked together, then the C++ compiler/linker must be used for linking (since special C++-ish things need to happen at link time like calling global constructors, instantiating templates, enabling exception support, etc.). However, the Fortran 77 intrinsic and run-time libraries must be linked in as well, but the C++ compiler/linker doesn't know by default how to add these Fortran 77 libraries. Hence, the macro @code{AC_F77_LIBRARY_LDFLAGS} was created to determine these Fortran 77 libraries. @end defmac @defmac AC_F77_WRAPPERS @maindex F77_WRAPPERS @cvindex F77_FUNC @cvindex F77_FUNC_ Defines C macros @code{F77_FUNC(name,NAME)} and @code{F77_FUNC_(name,NAME)} to properly mangle the names of C identifiers, and C identifiers with underscores, respectively, so that they match the name mangling scheme used by the Fortran 77 compiler. Fortran 77 is case-insensitive, and in order to achieve this the Fortran 77 compiler converts all identifiers into a canonical case and format. To call a Fortran 77 subroutine from C or to write a C function that is callable from Fortran 77, the C program must explicitly use identifiers in the format expected by the Fortran 77 compiler. In order to do this, one simply wraps all C identifiers in one of the macros provided by @code{AC_F77_WRAPPERS}. For example, suppose you have the following Fortran 77 subroutine: @example subroutine foobar(x,y) double precision x, y y = 3.14159 * x return end @end example You would then declare its prototype in C as: @example #ifdef F77_FUNC # define FOOBAR_F77 F77_FUNC(foobar,FOOBAR) #endif #ifdef __cplusplus extern "C" /* prevent C++ name mangling */ #endif void FOOBAR_F77(double *x, double *y); @end example Note that we pass both the lowercase and uppercase versions of the function name to @code{F77_FUNC} so that it can select the right one. Note also that all parameters to Fortran 77 routines are passed as pointers (@pxref{Mixing Fortran 77 With C and C++,,, automake, GNU Automake}). Although Autoconf tries to be intelligent about detecting the name-mangling scheme of the Fortran 77 compiler, there may be Fortran 77 compilers that it doesn't support yet. It is therefore recommended that you test whether the @code{F77_FUNC} and @code{F77_FUNC_} macros are defined, as we have done in the example above. Now, to call that routine from a C program, we would do something like: @example @{ double x = 2.7183, y; FOOBAR_F77(&x, &y); @} @end example If the Fortran 77 identifier contains an underscore (e.g. @code{foo_bar}), you should use @code{F77_FUNC_} instead of @code{F77_FUNC} (with the same arguments). This is because some Fortran 77 compilers mangle names differently if they contain an underscore. @end defmac @defmac AC_F77_FUNC (@var{name}, @ovar{shellvar}) @maindex F77_FUNC Given an identifier @var{name}, set the shell variable @var{shellvar} to hold the mangled version @var{name} according to the rules of the Fortran 77 linker (see also @code{AC_F77_WRAPPERS}). @var{shellvar} is optional; if it is not supplied, the shell variable will be simply @var{name}. The purpose of this macro is to give the caller a way to access the name-mangling information other than through the C preprocessor as above; for example, to call Fortran routines from some language other than C/C++. @end defmac @node System Services, UNIX Variants, Fortran 77 Compiler Characteristics, Existing Tests @section System Services The following macros check for operating system services or capabilities. @defmac AC_PATH_X @maindex PATH_X Try to locate the X Window System include files and libraries. If the user gave the command line options @option{--x-includes=@var{dir}} and @option{--x-libraries=@var{dir}}, use those directories. If either or both were not given, get the missing values by running @code{xmkmf} on a trivial @file{Imakefile} and examining the @file{Makefile} that it produces. If that fails (such as if @code{xmkmf} is not present), look for them in several directories where they often reside. If either method is successful, set the shell variables @code{x_includes} and @code{x_libraries} to their locations, unless they are in directories the compiler searches by default. If both methods fail, or the user gave the command line option @option{--without-x}, set the shell variable @code{no_x} to @samp{yes}; otherwise set it to the empty string. @end defmac @defmac AC_PATH_XTRA @maindex PATH_XTRA @ovindex X_CFLAGS @ovindex X_LIBS @ovindex X_EXTRA_LIBS @ovindex X_PRE_LIBS An enhanced version of @code{AC_PATH_X}. It adds the C compiler flags that X needs to output variable @code{X_CFLAGS}, and the X linker flags to @code{X_LIBS}. If X is not available, adds @option{-DX_DISPLAY_MISSING} to @code{X_CFLAGS}. This macro also checks for special libraries that some systems need in order to compile X programs. It adds any that the system needs to output variable @code{X_EXTRA_LIBS}. And it checks for special X11R6 libraries that need to be linked with before @option{-lX11}, and adds any found to the output variable @code{X_PRE_LIBS}. @c This is an incomplete kludge. Make a real way to do it. @c If you need to check for other X functions or libraries yourself, then @c after calling this macro, add the contents of @code{X_EXTRA_LIBS} to @c @code{LIBS} temporarily, like this: (FIXME - add example) @end defmac @defmac AC_SYS_INTERPRETER @maindex SYS_INTERPRETER Check whether the system supports starting scripts with a line of the form @samp{#! /bin/csh} to select the interpreter to use for the script. After running this macro, shell code in @code{configure.in} can check the shell variable @code{interpval}; it will be set to @samp{yes} if the system supports @samp{#!}, @samp{no} if not. @end defmac @defmac AC_SYS_LARGEFILE @maindex SYS_LARGEFILE @cvindex _FILE_OFFSET_BITS @cvindex _LARGEFILE_SOURCE @cvindex _LARGE_FILES @cvindex _XOPEN_SOURCE @ovindex CC Arrange for @uref{http://www.sas.com/standards/large.file/x_open.20Mar96.html, large-file support}. On some hosts, one must use special compiler options to build programs that can access large files. Append any such options to the output variable @code{CC}. Define @code{_FILE_OFFSET_BITS}, @code{_LARGEFILE_SOURCE}, @code{_LARGE_FILES}, and @code{_XOPEN_SOURCE} if necessary. The user can disable large-file support by configuring with the @option{--disable-largefile} option. If you use this macro, check that your program works even when @code{off_t} is longer than @code{long}, since this is common when large-file support is enabled. For example, it is not correct to print an arbitrary @code{off_t} value @code{X} with @code{printf ("%ld", (long) X)}. @end defmac @defmac AC_SYS_LONG_FILE_NAMES @maindex SYS_LONG_FILE_NAMES @cvindex HAVE_LONG_FILE_NAMES If the system supports file names longer than 14 characters, define @code{HAVE_LONG_FILE_NAMES}. @end defmac @defmac AC_SYS_POSIX_TERMIOS @maindex SYS_POSIX_TERMIOS @cindex POSIX termios headers @cindex termios POSIX headers Check to see if POSIX termios headers and functions are available on the system. If so, set the shell variable @code{am_cv_sys_posix_termios} to @samp{yes}. If not, set the variable to @samp{no}. @end defmac @defmac AC_SYS_RESTARTABLE_SYSCALLS @maindex SYS_RESTARTABLE_SYSCALLS @cvindex HAVE_RESTARTABLE_SYSCALLS If the system automatically restarts a system call that is interrupted by a signal, define @code{HAVE_RESTARTABLE_SYSCALLS}. This macro does not check if system calls are restarted in general--it tests whether a signal handler installed with @code{signal} (but not @code{sigaction}) causes system calls to be restarted. It does not test if system calls can be restarted when interrupted by signals that have no handler. @end defmac @node UNIX Variants, , System Services, Existing Tests @section UNIX Variants The following macros check for certain operating systems that need special treatment for some programs, due to exceptional oddities in their header files or libraries. These macros are warts; they will be replaced by a more systematic approach, based on the functions they make available or the environments they provide. @defmac AC_AIX @maindex AIX @cvindex _ALL_SOURCE If on AIX, define @code{_ALL_SOURCE}. Allows the use of some @sc{bsd} functions. Should be called before any macros that run the C compiler. @end defmac @defmac AC_ISC_POSIX @maindex ISC_POSIX @cvindex _POSIX_SOURCE @ovindex CC If on a POSIXized ISC @sc{unix}, define @code{_POSIX_SOURCE} and add @option{-posix} (for the @sc{gnu} C compiler) or @option{-Xp} (for other C compilers) to output variable @code{CC}. This allows the use of @sc{posix} facilities. Must be called after @code{AC_PROG_CC} and before any other macros that run the C compiler. @end defmac @defmac AC_MINIX @maindex MINIX @cvindex _MINIX @cvindex _POSIX_SOURCE @cvindex _POSIX_1_SOURCE If on Minix, define @code{_MINIX} and @code{_POSIX_SOURCE} and define @code{_POSIX_1_SOURCE} to be 2. This allows the use of @sc{posix} facilities. Should be called before any macros that run the C compiler. @end defmac @c ========================================================= Writing Tests @node Writing Tests, Results, Existing Tests, Top @chapter Writing Tests If the existing feature tests don't do something you need, you have to write new ones. These macros are the building blocks. They provide ways for other macros to check whether various kinds of features are available and report the results. This chapter contains some suggestions and some of the reasons why the existing tests are written the way they are. You can also learn a lot about how to write Autoconf tests by looking at the existing ones. If something goes wrong in one or more of the Autoconf tests, this information can help you understand the assumptions behind them, which might help you figure out how to best solve the problem. These macros check the output of the C compiler system. They do not cache the results of their tests for future use (@pxref{Caching Results}), because they don't know enough about the information they are checking for to generate a cache variable name. They also do not print any messages, for the same reason. The checks for particular kinds of C features call these macros and do cache their results and print messages about what they're checking for. When you write a feature test that could be applicable to more than one software package, the best thing to do is encapsulate it in a new macro. @xref{Writing Macros}, for how to do that. @menu * Examining Declarations:: Detecting header files and declarations * Examining Syntax:: Detecting language syntax features * Examining Libraries:: Detecting functions and global variables * Run Time:: Testing for run-time features * Portable Shell:: Shell script portability pitfalls * Multiple Cases:: Tests for several possible values * Language Choice:: Selecting which language to use for testing @end menu @node Examining Declarations, Examining Syntax, Writing Tests, Writing Tests @section Examining Declarations The macro @code{AC_TRY_CPP} is used to check whether particular header files exist. You can check for one at a time, or more than one if you need several header files to all exist for some purpose. @defmac AC_TRY_CPP (@var{includes}, @ovar{action-if-true}, @ovar{action-if-false}) @maindex TRY_CPP @var{includes} is C or C++ @code{#include} statements and declarations, on which shell variable, back quote, and backslash substitutions are performed. (Actually, it can be any C program, but other statements are probably not useful.) If the preprocessor produces no error messages while processing it, run shell commands @var{action-if-true}. Otherwise run shell commands @var{action-if-false}. This macro uses @code{CPPFLAGS}, but not @code{CFLAGS}, because @option{-g}, @option{-O}, etc. are not valid options to many C preprocessors. @end defmac Here is how to find out whether a header file contains a particular declaration, such as a typedef, a structure, a structure member, or a function. Use @code{AC_EGREP_HEADER} instead of running @code{grep} directly on the header file; on some systems the symbol might be defined in another header file that the file you are checking @samp{#include}s. @defmac AC_EGREP_HEADER (@var{pattern}, @var{header-file}, @var{action-if-found}, @ovar{action-if-not-found}) @maindex EGREP_HEADER If the output of running the preprocessor on the system header file @var{header-file} matches the @code{egrep} regular expression @var{pattern}, execute shell commands @var{action-if-found}, otherwise execute @var{action-if-not-found}. @end defmac To check for C preprocessor symbols, either defined by header files or predefined by the C preprocessor, use @code{AC_EGREP_CPP}. Here is an example of the latter: @example AC_EGREP_CPP(yes, [#ifdef _AIX yes #endif ], is_aix=yes, is_aix=no) @end example @defmac AC_EGREP_CPP (@var{pattern}, @var{program}, @ovar{action-if-found}, @ovar{action-if-not-found}) @maindex EGREP_CPP @var{program} is the text of a C or C++ program, on which shell variable, back quote, and backslash substitutions are performed. If the output of running the preprocessor on @var{program} matches the @code{egrep} regular expression @var{pattern}, execute shell commands @var{action-if-found}, otherwise execute @var{action-if-not-found}. This macro calls @code{AC_PROG_CPP} or @code{AC_PROG_CXXCPP} (depending on which language is current, @pxref{Language Choice}), if it hasn't been called already. @end defmac @node Examining Syntax, Examining Libraries, Examining Declarations, Writing Tests @section Examining Syntax To check for a syntax feature of the C, C++ or Fortran 77 compiler, such as whether it recognizes a certain keyword, use @code{AC_TRY_COMPILE} to try to compile a small program that uses that feature. You can also use it to check for structures and structure members that are not present on all systems. @defmac AC_TRY_COMPILE (@var{includes}, @var{function-body}, @ovar{action-if-found}, @ovar{action-if-not-found}) @maindex TRY_COMPILE Create a C, C++ or Fortran 77 test program (depending on which language is current, @pxref{Language Choice}), to see whether a function whose body consists of @var{function-body} can be compiled. For C and C++, @var{includes} is any @code{#include} statements needed by the code in @var{function-body} (@var{includes} will be ignored if the currently selected language is Fortran 77). This macro also uses @code{CFLAGS} or @code{CXXFLAGS} if either C or C++ is the currently selected language, as well as @code{CPPFLAGS}, when compiling. If Fortran 77 is the currently selected language then @code{FFLAGS} will be used when compiling. If the file compiles successfully, run shell commands @var{action-if-found}, otherwise run @var{action-if-not-found}. This macro does not try to link; use @code{AC_TRY_LINK} if you need to do that (@pxref{Examining Libraries}). @end defmac @node Examining Libraries, Run Time, Examining Syntax, Writing Tests @section Examining Libraries To check for a library, a function, or a global variable, Autoconf @code{configure} scripts try to compile and link a small program that uses it. This is unlike Metaconfig, which by default uses @code{nm} or @code{ar} on the C library to try to figure out which functions are available. Trying to link with the function is usually a more reliable approach because it avoids dealing with the variations in the options and output formats of @code{nm} and @code{ar} and in the location of the standard libraries. It also allows configuring for cross-compilation or checking a function's runtime behavior if needed. On the other hand, it can be slower than scanning the libraries once. A few systems have linkers that do not return a failure exit status when there are unresolved functions in the link. This bug makes the configuration scripts produced by Autoconf unusable on those systems. However, some of them can be given options that make the exit status correct. This is a problem that Autoconf does not currently handle automatically. If users encounter this problem, they might be able to solve it by setting @code{LDFLAGS} in the environment to pass whatever options the linker needs (for example, @option{-Wl,-dn} on @sc{mips risc/os}). @code{AC_TRY_LINK} is used to compile test programs to test for functions and global variables. It is also used by @code{AC_CHECK_LIB} to check for libraries (@pxref{Libraries}), by adding the library being checked for to @code{LIBS} temporarily and trying to link a small program. @defmac AC_TRY_LINK (@var{includes}, @var{function-body}, @ovar{action-if-found}, @ovar{action-if-not-found}) @maindex TRY_LINK Depending on the current language (@pxref{Language Choice}), create a test program to see whether a function whose body consists of @var{function-body} can be compiled and linked. For C and C++, @var{includes} is any @code{#include} statements needed by the code in @var{function-body} (@var{includes} will be ignored if the currently selected language is Fortran 77). This macro also uses @code{CFLAGS} or @code{CXXFLAGS} if either C or C++ is the currently selected language, as well as @code{CPPFLAGS}, when compiling. If Fortran 77 is the currently selected language then @code{FFLAGS} will be used when compiling. However, both @code{LDFLAGS} and @code{LIBS} will be used during linking in all cases. If the file compiles and links successfully, run shell commands @var{action-if-found}, otherwise run @var{action-if-not-found}. @end defmac @defmac AC_TRY_LINK_FUNC (@var{function}, @ovar{action-if-found}, @ovar{action-if-not-found}) @maindex TRY_LINK_FUNC Depending on the current language (@pxref{Language Choice}), create a test program to see whether a program whose body consists of a prototype of and a call to @var{function} can be compiled and linked. If the file compiles and links successfully, run shell commands @var{action-if-found}, otherwise run @var{action-if-not-found}. @end defmac @node Run Time, Portable Shell, Examining Libraries, Writing Tests @section Checking Run Time Behavior Sometimes you need to find out how a system performs at run time, such as whether a given function has a certain capability or bug. If you can, make such checks when your program runs instead of when it is configured. You can check for things like the machine's endianness when your program initializes itself. If you really need to test for a run-time behavior while configuring, you can write a test program to determine the result, and compile and run it using @code{AC_TRY_RUN}. Avoid running test programs if possible, because using them prevents people from configuring your package for cross-compiling. @menu * Test Programs:: Running test programs * Guidelines:: General rules for writing test programs * Test Functions:: Avoiding pitfalls in test programs @end menu @node Test Programs, Guidelines, Run Time, Run Time @subsection Running Test Programs Use the following macro if you need to test run-time behavior of the system while configuring. @defmac AC_TRY_RUN (@var{program}, @ovar{action-if-true}, @ovar{action-if-false}, @ovar{action-if-cross-compiling}) @maindex TRY_RUN @var{program} is the text of a C program, on which shell variable and back quote substitutions are performed. If it compiles and links successfully and returns an exit status of 0 when executed, run shell commands @var{action-if-true}. Otherwise run shell commands @var{action-if-false}; the exit status of the program is available in the shell variable @samp{$?}. This macro uses @code{CFLAGS} or @code{CXXFLAGS}, @code{CPPFLAGS}, @code{LDFLAGS}, and @code{LIBS} when compiling. If the C compiler being used does not produce executables that run on the system where @code{configure} is being run, then the test program is not run. If the optional shell commands @var{action-if-cross-compiling} are given, they are run instead. Otherwise, @code{configure} prints an error message and exits. @end defmac Try to provide a pessimistic default value to use when cross-compiling makes run-time tests impossible. You do this by passing the optional last argument to @code{AC_TRY_RUN}. @code{autoconf} prints a warning message when creating @code{configure} each time it encounters a call to @code{AC_TRY_RUN} with no @var{action-if-cross-compiling} argument given. You may ignore the warning, though users will not be able to configure your package for cross-compiling. A few of the macros distributed with Autoconf produce this warning message. To configure for cross-compiling you can also choose a value for those parameters based on the canonical system name (@pxref{Manual Configuration}). Alternatively, set up a test results cache file with the correct values for the host system (@pxref{Caching Results}). To provide a default for calls of @code{AC_TRY_RUN} that are embedded in other macros, including a few of the ones that come with Autoconf, you can call @code{AC_PROG_CC} before running them. Then, if the shell variable @code{cross_compiling} is set to @samp{yes}, use an alternate method to get the results instead of calling the macros. @node Guidelines, Test Functions, Test Programs, Run Time @subsection Guidelines for Test Programs Test programs should not write anything to the standard output. They should return 0 if the test succeeds, nonzero otherwise, so that success can be distinguished easily from a core dump or other failure; segmentation violations and other failures produce a nonzero exit status. Test programs should @code{exit}, not @code{return}, from @code{main}, because on some systems (old Suns, at least) the argument to @code{return} in @code{main} is ignored. Test programs can use @code{#if} or @code{#ifdef} to check the values of preprocessor macros defined by tests that have already run. For example, if you call @code{AC_HEADER_STDC}, then later on in @file{configure.in} you can have a test program that includes an @sc{ansi} C header file conditionally: @example @group #if STDC_HEADERS # include #endif @end group @end example If a test program needs to use or create a data file, give it a name that starts with @file{conftest}, such as @file{conftestdata}. The @code{configure} script cleans up by running @samp{rm -rf conftest*} after running test programs and if the script is interrupted. @node Test Functions, , Guidelines, Run Time @subsection Test Functions Function declarations in test programs should have a prototype conditionalized for C++. In practice, though, test programs rarely need functions that take arguments. @example #ifdef __cplusplus foo (int i) #else foo (i) int i; #endif @end example Functions that test programs declare should also be conditionalized for C++, which requires @samp{extern "C"} prototypes. Make sure to not include any header files containing clashing prototypes. @example #ifdef __cplusplus extern "C" void *malloc (size_t); #else char *malloc (); #endif @end example If a test program calls a function with invalid parameters (just to see whether it exists), organize the program to ensure that it never invokes that function. You can do this by calling it in another function that is never invoked. You can't do it by putting it after a call to @code{exit}, because GCC version 2 knows that @code{exit} never returns and optimizes out any code that follows it in the same block. If you include any header files, make sure to call the functions relevant to them with the correct number of arguments, even if they are just 0, to avoid compilation errors due to prototypes. GCC version 2 has internal prototypes for several functions that it automatically inlines; for example, @code{memcpy}. To avoid errors when checking for them, either pass them the correct number of arguments or redeclare them with a different return type (such as @code{char}). @node Portable Shell, Multiple Cases, Run Time, Writing Tests @section Portable Shell Programming When writing your own checks, there are some shell script programming techniques you should avoid in order to make your code portable. The Bourne shell and upward-compatible shells like Bash and the Korn shell have evolved over the years, but to prevent trouble, do not take advantage of features that were added after @sc{unix} version 7, circa 1977. You should not use shell functions, aliases, negated character classes, or other features that are not found in all Bourne-compatible shells; restrict yourself to the lowest common denominator. Even @code{unset} is not supported by all shells! Also, include a space after the exclamation point in interpreter specifications, like this: @example #! /usr/bin/perl @end example @noindent If you omit the space before the path, then 4.2@sc{bsd} based systems (such as Sequent DYNIX) will ignore the line, because they interpret @samp{#! /} as a 4-byte magic number. The set of external programs you should run in a @code{configure} script is fairly small. @xref{Utilities in Makefiles,, Utilities in Makefiles, standards, GNU Coding Standards}, for the list. This restriction allows users to start out with a fairly small set of programs and build the rest, avoiding too many interdependencies between packages. Some of these external utilities have a portable subset of features, see @ref{Limitations of Usual Tools}. @menu * Shellology:: A zoology of shells * Special Shell Variables:: Variables you should not change * Shell Substitutions:: Test and assign * Limitations of Builtins:: Portable use of not so portable /bin/sh * Limitations of Usual Tools:: Portable use of portable tools @end menu @node Shellology, Special Shell Variables, Portable Shell, Portable Shell @subsection Shellology There are several families of shells, most prominently the Bourne family and the C shell family which are deeply incompatible. If you want to write portable shell scripts, avoid members of the C shell family. Below we describe some of the members of the Bourne shell family. @table @asis @item @command{bash} @cindex @command{bash} To detect whether you are running @command{bash}, test if @code{BASH_VERSION} is set. To disable its extensions and require @sc{posix} compatibility, run @samp{set -o posix}. @xref{Bash POSIX Mode,, Bash @sc{posix} Mode, bash, The GNU Bash Reference Manual}, for details. @item @command{zsh} @cindex @command{zsh} To detect whether you are running @command{zsh}, test if @code{ZSH_VERSION} is set. By default @command{zsh} is @emph{not} compatible with the Bourne shell: you have to run @samp{emulate sh} and set @code{NULLCMD} to @samp{:}. @xref{Compatibility,, Compatibility, zsh, The Z Shell Manual}, for details. @item @command{ash} @cindex @command{ash} @command{ash} is often used on @sc{gnu}/Linux and @sc{bsd} systems as a light-weight Bourne-compatible shell. @command{ash} version 0.2 has some bugs that are fixed in the 0.3.x series, but portable shell scripts should workaround them, since version 0.2 is still shipped with many @sc{gnu}/Linux distributions. To be compatible with @command{ash} 0.2 @itemize @bullet @item don't rely on variable assignment setting @samp{$?} unless the assignment involves command substitution: @example false || foo=bar && echo "Not portable" false || foo=`bar` && echo "Portable" @end example @item don't use @samp{$?} after expanding empty or unset variables: @example foo= false $foo echo "Don't use it: $?" @end example @item don't use command substitution within variable expansion: @example echo $@{FOO=`bar`@} @end example @item beware that @command{exit} inside command substitution causes the current shell exit as well. Use parentheses to prevent @command{ash} from exiting: @example (`exit 1`) || echo "All right" `exit 1` || echo "ash won't print it" @end example @end itemize @end table @node Special Shell Variables, Shell Substitutions, Shellology, Portable Shell @subsection Special Shell Variables Some shell variables shall not be used or have a deep influence on the behavior of the shell. In order to recover a sane behavior from the shell, some variables should be unset, but @command{unset} is not portable (@pxref{Limitations of Builtins}) and a fall back value is needed. We list these values below. @c Alphabetical order, case insensitive, `A' before `a'. @table @code @item CDPATH @evindex CDPATH Because when this variable is set @code{cd} is verbose, idioms such as @samp{abs=`cd $rel && pwd`} break, since @code{abs} receives twice the path. @c FIXME: Which shells? How do they behave? Setting @code{CDPATH} to the empty value is not enough for most shells. A simple colon is enough but for @code{zsh}, which prefers a leading dot: @example zsh-3.1.6 % mkdir foo && (CDPATH=: cd foo) /tmp/foo zsh-3.1.6 % (CDPATH=:. cd foo) /tmp/foo zsh-3.1.6 % (CDPATH=.: cd foo) zsh-3.1.6 % @end example @noindent (of course we could just @code{unset} @code{CDPATH}, it also behaves properly if set to the empty string). Life wouldn't be so much fun if @command{bash} and @command{zsh} had the same behavior: @example bash-2.02 % (CDPATH=:. cd foo) bash-2.02 % (CDPATH=.: cd foo) /tmp/foo @end example Therefore a portable solution to neutralize @samp{CDPATH} is @samp{CDPATH=$@{ZSH_VERSION+.@}:}. Note that since @command{zsh} support @command{unset}, you may unset @samp{CDPATH} using @samp{:} as a fall back, see @ref{Limitations of Builtins}. @item LANG @itemx LC_ALL @itemx LC_TIME @itemx LC_CTYPE @itemx LANGUAGE @itemx LC_COLLATE @itemx LC_NUMERIC @itemx LC_MESSAGES @evindex LANG @evindex LC_ALL @evindex LC_TIME @evindex LC_CTYPE @evindex LANGUAGE @evindex LC_COLLATE @evindex LC_NUMERIC @evindex LC_MESSAGES These must not be set unconditionally because not all systems understand e.g. @samp{LANG=C} (notably SCO). Fixing @env{LC_MESSAGES} prevents Solaris @command{sh} from translating var values in @code{set}! Non-C @env{LC_CTYPE} values break the ctype check. Fixing @env{LC_COLLATE} makes scripts more portable in some cases. For example, it causes the regular expression @samp{[a-z]} to match only lower-case letters on @sc{ascii} platforms. However, @samp{[a-z]} does not work in general even when @env{LC_COLLATE} is fixed; for example, it does not work for @sc{ebcdic} platforms. For maximum portability, you should use regular expressions like @samp{[abcdefghijklmnopqrstuvwxyz]} that list characters explicitly instead of relying on ranges. @emph{If} one of these variables is set, you should try to unset it, using @samp{C} as a fall back value. see @ref{Limitations of Builtins}, builtin @command{unset}, for more details. @item NULLCMD @evindex NULLCMD When executing the command @samp{>foo}, @command{zsh} executes @samp{$NULLCMD >foo}. The Bourne shell considers @code{NULLCMD} is @samp{:}, while @command{zsh}, even in Bourne shell compatibility mode, sets @code{NULLCMD} to @samp{cat}. If you forgot to set @code{NULLCMD}, your script might be suspended waiting for data on its standard input. @item status @evindex status This variable is an alias to @samp{$?} for @code{zsh} (at least 3.1.6), hence read-only. Do not use it. @end table @node Shell Substitutions, Limitations of Builtins, Special Shell Variables, Portable Shell @subsection Shell Substitutions A nonportable shell programming construct is @example @var{var}=$@{@var{var}:-@var{value}@} @end example @noindent The intent is to set @var{var} to @var{value} only if it is not already set, but if @var{var} has any value, even the empty string, to leave it alone. Old @sc{bsd} shells, including the Ultrix @code{sh}, don't accept the colon for any shell substitution, and complain and die. A portable equivalent is @example : $@{@var{var}=@var{value}@} @end example If the value is a literal string, it should be quoted: @example : $@{var='Some words'@} @end example @noindent otherwise some shells, such as on Digital Unix V 5.0, will die because of a ``bad substitution''. When setting several variables in a row, be aware that the order of the evaluation is undefined. For instance @samp{foo=1 foo=2; echo $foo} gives @samp{1} with sh on Solaris, but @samp{2} with Bash. You must use @samp{;} to enforce the order: @samp{foo=1; foo=2; echo $foo}. @cindex @samp{"$@@"} One of the most famous shell portability issues is related to @samp{"$@@"}: when there are no positional argument, it is supposed to be equivalent to nothing. But some shell, for instance under Digital Unix 4.0 and 5.0, will then replace it with an empty argument. To be portable, use @samp{$@{1+"$@@"@}}. Contrary to a persistent urban legend, the Bourne shell does not systematically split variables and backquoted expressions, in particular, the following code: @example case "$given_srcdir" in .) top_srcdir="`echo "$dots" | sed 's,/$,,'`" *) top_srcdir="$dots$given_srcdir" ;; esac @end example @noindent is more readable with the right-hand side of the assignments, and the argument of @code{case} left without quotes: @example case $given_srcdir in .) top_srcdir=`echo "$dots" | sed 's,/$,,'` *) top_srcdir=$dots$given_srcdir ;; esac @end example @noindent and in fact it is even @emph{more} portable: in the first case of the first attempt, the computation of @code{top_srcdir} is not portable, since not all the shells understand properly @samp{"`... "foo"... `"}. Worse yet, not all the shells understand @samp{"`... \"foo\"... `"} the same way: there is just no portable way to use double-quoted strings inside double-quoted backquoted expressions (Pfew!). @node Limitations of Builtins, Limitations of Usual Tools, Shell Substitutions, Portable Shell @subsection Limitations of Shell Builtins No no, we are serious: some shells do have limitations :) You should always keep in mind that any built-in or command may support options, and therefore have a very different behavior with arguments starting with a dash. For instance, the innocent @samp{echo "$word"} can give unexpected results when @code{word} starts with a dash. It is often possible to avoid this problem using @samp{echo "x$word"}, taking the @samp{x} into account later in the pipe. @table @asis @item @command{!} @cindex @command{!} You can't use @command{!}, you'll have to rewrite your code. @item @command{break} @cindex @command{break} The use of @samp{break 2} etc. is safe. @item @command{case} @cindex @command{case} You don't need to quote the argument, no splitting is performed. You don't need the last @samp{;;}, but you should use it. Because of a bug in its @code{fnmatch}, @command{bash} fails to handle properly backslashes in character classes: @example bash-2.02$ case /tmp in [/\\]*) echo OK;; esac bash-2.02$ @end example @noindent This is extremely unfortunate, since you are likely to use this code to handle @sc{unix} or @sc{ms-dos} absolute paths. To workaround this bug, always put the backslash first: @example bash-2.02$ case '\TMP' in [\\/]*) echo OK;; esac OK bash-2.02$ case /tmp in [\\/]*) echo OK;; esac OK @end example @item @command{echo} @cindex @command{echo} The simple @code{echo} is probably the most surprising source of portability troubles. Don't expect any option. @xref{Preset Output Variables}, @code{ECHO_N} etc. for a means to simulate @option{-c}. Do not use backslashes in the arguments, as there is no consensus on their handling: On @samp{echo '\n' | wc -l}, the @command{sh} of Digital Unix 4.0, @sc{mips risc/os} 4.52, answer 2, but the Solaris' @command{sh}, Bash and Zsh (in @command{sh} emulation mode) report 1. Please note that the problem is truly @command{echo}: all the shells understand @samp{'\n'} as the string composed of a backslash and an n. @item @command{exit} @cindex @command{exit} Some shell scripts, such as those generated by @command{autoconf}, use a trap to clean up before exiting. If the last shell command exited with nonzero status, the trap also exits with nonzero status so that the invoker can tell that an error occurred. Unfortunately, in some shells, such as Solaris 8 @command{sh}, an exit trap ignores the @code{exit} command's status. In these shells, a trap cannot determine whether it was invoked by plain @code{exit} or by @code{exit 1}. To work around this problem, use @code{(exit 1); exit} instead of @samp{exit 1}. @item @command{export} @cindex @command{export} The builtin @command{export} dubs @dfn{environment variable} a shell variable. Each update of exported variables corresponds to an update of the environment variables. Conversely, each environment variable received by the shell when it is launched should be imported as a shell variable marked as exported. Alas, pretty many shells, such as Solaris 2.5, IRIX 6.3, IRIX 5.2, AIX 4.1.5 and DU 4.0 forget to @command{export} the environment variables they receive. As a result two variables are coexisting: the environment variable, and the shell variable. The following code demonstrates this failure: @example #! /bin/sh echo $FOO FOO=bar echo $FOO exec /bin/sh $0 @end example @noindent when run with @samp{FOO=foo} in the environment, these shells will print alternately @samp{foo} and @samp{bar}, although it should only print @samp{foo} and then a sequence of @samp{bar}s. Therefore you should @command{export} again each environment variable you update. @item @command{if} @cindex @command{if} Using @samp{!} is not portable. Instead of @example if ! cmp -s file file.new; then mv file.new file fi @end example @noindent use @example if cmp -s file file.new; then :; else mv file.new file fi @end example @item @command{set} @cindex @command{set} This builtin faces the usual problem with arguments starting with a dash. Modern shells, such as Bash or Zsh understand @samp{--} to specify the end of the options (any argument behind @samp{--} is an parameters, even @samp{-x} for instance), but most shell simply stop the option processing as soon as a non option argument is found. Therefore use @samp{dummy} or simply @samp{x} to neutralize the option processing, and use @command{shift} to pop it out: @example set x $my_list; shift @end example @item @command{shift} @cindex @command{shift} Not only is @command{shift}ing a bad idea when there is nothing left to shift, but in addition it is not portable: the shell of @sc{mips risc/os} 4.52 refuses it. @item @command{test} @cindex @command{test} The @code{test} program is the way to perform many file and string tests. It is often invoked by the alternate name @samp{[}, but using that name in Autoconf code is asking for trouble since it is an M4 quote character. If you need to make multiple checks using @code{test}, combine them with the shell operators @samp{&&} and @samp{||} instead of using the @code{test} operators @option{-a} and @option{-o}. On System V, the precedence of @option{-a} and @option{-o} is wrong relative to the unary operators; consequently, @sc{posix} does not specify them, so using them is nonportable. If you combine @samp{&&} and @samp{||} in the same statement, keep in mind that they have equal precedence. You may use @samp{!} with @command{test}, but not with @command{if}: @samp{test ! -r foo || exit 1}. @item @command{test} (files) To enable @code{configure} scripts to support cross-compilation, they shouldn't do anything that tests features of the build system instead of the host system. But occasionally you may find it necessary to check whether some arbitrary file exists. To do so, use @samp{test -f} or @samp{test -r}. Do not use @samp{test -x}, because @sc{4.3bsd} does not have it. Do not use @samp{test -e} either, because Solaris 2.5 does not have it. @item @command{test} (strings) Avoid @samp{test "@var{string}"}, in particular if @var{string} might start with a dash, since @code{test} might interpret its argument as an option (e.g., @samp{@var{string} = "-n"}). Contrary to a common belief, @samp{test -n @var{string}} and @samp{test -z @var{string}} @strong{are} portable, nevertheless many shells (such as Solaris 2.5, AIX 3.2, UNICOS 10.0.0.6, Digital Unix 4 etc.) have bizarre precedence and may be confused if @var{string} looks like an operator: @example $ test -n = test: argument expected @end example If there are risks, use @samp{test "x@var{string}" = x} or @samp{test "x@var{string}" != x} instead. It is frequent to find variations of the following idiom: @example test -n "`echo $ac_feature | sed 's/[-a-zA-Z0-9_]//g'`" && @var{action} @end example @noindent to take an action when a token matches a given pattern. Such constructs are always avoidable, and should always be. Rather, use: @example echo "$ac_feature" | grep '[^-a-zA-Z0-9_]' >/dev/null 2>&1 && @var{action} @end example @noindent Where possible, use @code{case} since, being a shell builtin, it is faster: @example case $ac_feature in *[!-a-zA-Z0-9_]*) @var{action};; esac @end example Alas, negated character classes are probably not portable, although no shell is known not to support the @sc{posix.2} syntax @samp{[!...]} (when in interactive mode, @command{zsh} is confused by the @samp{[!...]} syntax and looks for an event in its history because of @samp{!}). Many shells do not support the alternative syntax @samp{[^...]} (Solaris, Digital Unix etc.). One solution can be: @example expr "$ac_feature" : '.*[^-a-zA-Z0-9_]' >/dev/null && @var{action} @end example @noindent or better yet @example expr "x$ac_feature" : '.*[^-a-zA-Z0-9_]' >/dev/null && @var{action} @end example @samp{expr "X@var{foo}" : "X@var{bar}"} is more robust than @samp{echo "X@var{foo}" | grep "^X@var{bar}"}, because it avoids problems when @samp{@var{foo}} contains backslashes. @item @command{unset} @cindex @command{unset} You cannot assume the support of @command{unset}, nevertheless, because it is extremely useful to disable embarrassing variables such as @code{CDPATH} or @code{LANG}, you can test for its existence, and use it @emph{provided} you give a neutralizing value when @command{unset} is not supported: @example if (unset FOO) >/dev/null 2>&1; then unset=unset else unset=false fi $unset CDPATH || CDPATH=: @end example @xref{Special Shell Variables}, for some neutralizing values. Also, see @ref{Limitations of Builtins}, documentation of @command{export}, for the case of environment variables. @end table @node Limitations of Usual Tools, , Limitations of Builtins, Portable Shell @subsection Limitations of Usual Tools The small set of tools you can expect to find on any machine can still find some limitations you should be aware of. @table @asis @item @command{awk} @cindex @command{awk} Don't leave white spaces before the parentheses in user functions calls, @sc{gnu} awk will reject it: @example $ gawk 'function die () @{ print "Aaaaarg!" @} BEGIN @{ die () @}' gawk: cmd. line:2: BEGIN @{ die () @} gawk: cmd. line:2: ^ parse error $ gawk 'function die () @{ print "Aaaaarg!" @} BEGIN @{ die() @}' Aaaaarg! @end example @item @command{cat} @cindex @command{cat} Don't rely on any option. @item @command{egrep} @cindex @command{egrep} The empty alternative is not portable, use @samp{?} instead. For instance with Digital Unix v5.0: @example > printf "foo\n|foo\n" | egrep '^(|foo|bar)$' |foo > printf "bar\nbar|\n" | egrep '^(foo|bar|)$' bar| > printf "foo\nfoo|\n|bar\nbar\n" | egrep '^(foo||bar)$' foo |bar @end example @command{egrep} also suffers the limitations of @command{grep}. @item @command{expr} @cindex @command{expr} No @command{expr} keyword starts with @samp{x}, so use @samp{expr x"@var{word}" : '@var{regex}'} to keep @command{expr} from misinterpreting @var{word}. You can use @samp{|}. There is one portability problem occuring when you @samp{|} together the empty string (or zero) with the empty string. For example: @example expr '' \| '' @end example @sc{gnu}/Linux and @sc{posix.2} return the empty string for this case, but traditional Unix returns @samp{0}. In the latest @sc{posix} draft, the specification has been changed to match traditional Unix's behavior (which is bizarre, but it's too late to fix this). Avoid this portability problem by avoiding the empty string. Don't use @code{length}, @code{substr}, @code{match} and @code{index}. @item @command{expr} (@samp{:}) @cindex @command{expr} Don't use @samp{\?}, @samp{\+} and @samp{\|} in patterns, they are not supported on Solaris. Older @command{expr} implementations (e.g. SunOS 4 @command{expr} and Solaris 8 @command{/usr/ucb/expr}) have a silly length limit that causes @command{expr} to fail if the matched substring is longer than 120 bytes. In this case, you might want to fall back on @samp{echo|sed} if @command{expr} fails. @item @command{grep} @cindex @command{grep} Don't use @samp{grep -s} to suppress output, because @samp{grep -s} on System V does not suppress output, only error messages. Instead, redirect the standard output and standard error (in case the file doesn't exist) of @code{grep} to @file{/dev/null}. Check the exit status of @code{grep} to determine whether it found a match. Don't use multiple regexps with @option{-e}, as some @code{grep} will only honor the last pattern (eg., IRIX 6.5 and Solaris 2.5.1). Anyway, Stardent Vistra SVR4 @code{grep} lacks @option{-e}... Instead, use alternation and @code{egrep}. @item @command{ln} @cindex @command{ln} Don't rely on @command{ln} having a @option{-f} option. Symbolic links are not available on old systems, use @samp{ln} as a fall back. The @sc{djgpp} @command{ln} emulates soft links for executables by generating a stub that in turn calls the real program. This feature also works with nonexistent files like in the Unix spec. So @samp{ln -s src dst} will generate @file{src.exe} which will attempt to call @file{dst.exe}. But this feature only works for executables, therefore, don't rely on symbolic links on @sc{djgpp}. @item @command{sed} @cindex @command{sed} Of course the option @option{-e} is portable, but it is not needed. No valid @command{sed} program can start with a dash, so it does not help disambiguating. Its sole usefulness is helping enforcing indenting as in: @example sed -e @var{instruction-1} \ -e @var{instruction-2} @end example @noindent as opposed to @example sed @var{instruction-1};@var{instruction-2} @end example @command{sed} scripts should not use branch labels longer than 8 characters and should not contain comments. @command{sed} input should have reasonably long lines, since some @command{sed} have an input buffer limited to 4000 bytes. Alternation, @samp{\|}, is common but not portable. Nested groups are extremely portable, but there is at least one @command{sed} (System V/68 Base Operating System R3V7.1) that does not support it. Anchors (@samp{^} and @samp{$}) inside groups are not portable. @c FIXME: I know Solaris is guilty, but I don't remember how. @item @command{sed} (@samp{t}) @cindex @command{sed} (@samp{t}) Some old systems have @command{sed} that ``forget'' to reset their @samp{t} flag when starting a new cycle. For instance on @sc{mips risc/os}, and on @sc{irix} 5.3, if you run the following @command{sed} script (the line numbers are not actual part of the texts): @example s/keep me/kept/g # a t end # b s/.*/deleted/g # c : end # d @end example @noindent on @example delete me # 1 delete me # 2 keep me # 3 delete me # 4 @end example @noindent you get @example deleted delete me kept deleted @end example @noindent instead of @example deleted deleted kept deleted @end example Why? When processing 1, a matches, therefore sets the t flag, b jumps to d, and the output is produced. When processing line 2, the t flag is still set (this is the bug). Line a fails to match, but @command{sed} is not supposed to clear the t flag when a substitution fails. Line b sees that the flag is set, therefore it clears it, and jumps to d, hence you get @samp{delete me} instead of @samp{deleted}. When processing 3 t is clear, a matches, so the flag is set, hence b clears the flags and jumps. Finally, since the flag is clear, 4 is processed properly. There are two things one should remind about @samp{t} in @command{sed}. Firstly, always remember that @samp{t} jumps if @emph{some} substitution succeeded, not only the immediately preceding substitution, therefore, always use a fake @samp{t clear; : clear} to reset the t flag where indeed. Secondly, you cannot rely on @command{sed} to clear the flag at each new cycle. One portable implementation of the script above is: @example t clear : clear s/keep me/kept/g t end s/.*/deleted/g : end @end example @end table @node Multiple Cases, Language Choice, Portable Shell, Writing Tests @section Multiple Cases Some operations are accomplished in several possible ways, depending on the @sc{unix} variant. Checking for them essentially requires a ``case statement''. Autoconf does not directly provide one; however, it is easy to simulate by using a shell variable to keep track of whether a way to perform the operation has been found yet. Here is an example that uses the shell variable @code{fstype} to keep track of whether the remaining cases need to be checked. @example @group AC_MSG_CHECKING(how to get file system type) fstype=no # The order of these tests is important. AC_TRY_CPP([#include #include ], [AC_DEFINE(FSTYPE_STATVFS) fstype=SVR4]) if test $fstype = no; then AC_TRY_CPP([#include #include ], [AC_DEFINE(FSTYPE_USG_STATFS) fstype=SVR3]) fi if test $fstype = no; then AC_TRY_CPP([#include #include ], [AC_DEFINE(FSTYPE_AIX_STATFS) fstype=AIX]) fi # (more cases omitted here) AC_MSG_RESULT($fstype) @end group @end example @node Language Choice, , Multiple Cases, Writing Tests @section Language Choice @cindex Language Packages that use both C and C++ need to test features of both compilers. Autoconf-generated @code{configure} scripts check for C features by default. The following macros determine which language's compiler is used in tests that follow in @file{configure.in}. @defmac AC_LANG (@var{language}) Do compilation tests using the compiler, preprocessor and file extensions for the @var{language}. Supported languages are: @table @samp @item C Do compilation tests using @code{CC} and @code{CPP} and use extension @file{.c} for test programs. @item C++ Do compilation tests using @code{CXX} and @code{CXXCPP} and use extension @file{.C} for test programs. @item Fortran 77 Do compilation tests using @code{F77} and use extension @file{.f} for test programs. @end table @end defmac @defmac AC_LANG_PUSH (@var{language}) @maindex LANG_PUSH Remember the current language (as set by @code{AC_LANG}) on a stack, and then select the @var{language}. Use this macro and @code{AC_LANG_POP} in macros that need to temporarily switch to a particular language. @end defmac @defmac AC_LANG_POP @maindex LANG_POP Select the language that is saved on the top of the stack, as set by @code{AC_LANG_PUSH}, and remove it from the stack. @end defmac @defmac AC_REQUIRE_CPP @maindex REQUIRE_CPP Ensure that whichever preprocessor would currently be used for tests has been found. Calls @code{AC_REQUIRE} (@pxref{Prerequisite Macros}) with an argument of either @code{AC_PROG_CPP} or @code{AC_PROG_CXXCPP}, depending on which language is current. @end defmac @c ====================================================== Results of Tests. @node Results, Writing Macros, Writing Tests, Top @chapter Results of Tests Once @code{configure} has determined whether a feature exists, what can it do to record that information? There are four sorts of things it can do: define a C preprocessor symbol, set a variable in the output files, save the result in a cache file for future @code{configure} runs, and print a message letting the user know the result of the test. @menu * Defining Symbols:: Defining C preprocessor symbols * Setting Output Variables:: Replacing variables in output files * Caching Results:: Speeding up subsequent @code{configure} runs * Printing Messages:: Notifying @code{configure} users @end menu @node Defining Symbols, Setting Output Variables, Results, Results @section Defining C Preprocessor Symbols A common action to take in response to a feature test is to define a C preprocessor symbol indicating the results of the test. That is done by calling @code{AC_DEFINE} or @code{AC_DEFINE_UNQUOTED}. By default, @code{AC_OUTPUT} places the symbols defined by these macros into the output variable @code{DEFS}, which contains an option @option{-D@var{symbol}=@var{value}} for each symbol defined. Unlike in Autoconf version 1, there is no variable @code{DEFS} defined while @code{configure} is running. To check whether Autoconf macros have already defined a certain C preprocessor symbol, test the value of the appropriate cache variable, as in this example: @example AC_CHECK_FUNC(vprintf, [AC_DEFINE(HAVE_VPRINTF)]) if test "$ac_cv_func_vprintf" != yes; then AC_CHECK_FUNC(_doprnt, [AC_DEFINE(HAVE_DOPRNT)]) fi @end example If @code{AC_CONFIG_HEADERS} has been called, then instead of creating @code{DEFS}, @code{AC_OUTPUT} creates a header file by substituting the correct values into @code{#define} statements in a template file. @xref{Configuration Headers}, for more information about this kind of output. @defmac AC_DEFINE (@var{variable}, @ovar{value}, @ovar{description}) @maindex DEFINE Define C preprocessor variable @var{variable}. If @var{value} is given, set @var{variable} to that value (verbatim), otherwise set it to 1. @var{value} should not contain literal newlines, and if you are not using @code{AC_CONFIG_HEADERS} it should not contain any @samp{#} characters, as @code{make} tends to eat them. To use a shell variable (which you need to do in order to define a value containing the M4 quote characters @samp{[} or @samp{]}), use @code{AC_DEFINE_UNQUOTED} instead. @var{description} is only useful if you are using @code{AC_CONFIG_HEADERS}. In this case, @var{description} is put into the generated @file{config.h.in} as the comment before the macro define; the macro need not be mentioned in @file{acconfig.h}. The following example defines the C preprocessor variable @code{EQUATION} to be the string constant @samp{"$a > $b"}: @example AC_DEFINE(EQUATION, "$a > $b") @end example @end defmac @defmac AC_DEFINE_UNQUOTED (@var{variable}, @ovar{value}, @ovar{description}) @maindex DEFINE_UNQUOTED Like @code{AC_DEFINE}, but three shell expansions are performed---once---on @var{variable} and @var{value}: variable expansion (@samp{$}), command substitution (@samp{`}), and backslash escaping (@samp{\}). Single and double quote characters in the value have no special meaning. Use this macro instead of @code{AC_DEFINE} when @var{variable} or @var{value} is a shell variable. Examples: @example AC_DEFINE_UNQUOTED(config_machfile, "$machfile") AC_DEFINE_UNQUOTED(GETGROUPS_T, $ac_cv_type_getgroups) AC_DEFINE_UNQUOTED($ac_tr_hdr) @end example @end defmac Due to the syntactical bizarreness of the Bourne shell, do not use semicolons to separate @code{AC_DEFINE} or @code{AC_DEFINE_UNQUOTED} calls from other macro calls or shell code; that can cause syntax errors in the resulting @code{configure} script. Use either spaces or newlines. That is, do this: @example AC_CHECK_HEADER(elf.h, [AC_DEFINE(SVR4) LIBS="$LIBS -lelf"]) @end example @noindent or this: @example AC_CHECK_HEADER(elf.h, [AC_DEFINE(SVR4) LIBS="$LIBS -lelf"]) @end example @noindent instead of this: @example AC_CHECK_HEADER(elf.h, [AC_DEFINE(SVR4); LIBS="$LIBS -lelf"]) @end example @node Setting Output Variables, Caching Results, Defining Symbols, Results @section Setting Output Variables One way to record the results of tests is to set @dfn{output variables}, which are shell variables whose values are substituted into files that @code{configure} outputs. The two macros below create new output variables. @xref{Preset Output Variables}, for a list of output variables that are always available. @defmac AC_SUBST (@var{variable}, @ovar{value}) @maindex SUBST Create an output variable from a shell variable. Make @code{AC_OUTPUT} substitute the variable @var{variable} into output files (typically one or more @file{Makefile}s). This means that @code{AC_OUTPUT} will replace instances of @samp{@@@var{variable}@@} in input files with the value that the shell variable @var{variable} has when @code{AC_OUTPUT} is called. This value of @var{variable} should not contain literal newlines. If @var{value} is given, in addition assign it to @samp{variable}. @end defmac @defmac AC_SUBST_FILE (@var{variable}) @maindex SUBST_FILE Another way to create an output variable from a shell variable. Make @code{AC_OUTPUT} insert (without substitutions) the contents of the file named by shell variable @var{variable} into output files. This means that @code{AC_OUTPUT} will replace instances of @samp{@@@var{variable}@@} in output files (such as @file{Makefile.in}) with the contents of the file that the shell variable @var{variable} names when @code{AC_OUTPUT} is called. Set the variable to @file{/dev/null} for cases that do not have a file to insert. This macro is useful for inserting @file{Makefile} fragments containing special dependencies or other @code{make} directives for particular host or target types into @file{Makefile}s. For example, @file{configure.in} could contain: @example AC_SUBST_FILE(host_frag) host_frag=$srcdir/conf/sun4.mh @end example @noindent and then a @file{Makefile.in} could contain: @example @@host_frag@@ @end example @end defmac @node Caching Results, Printing Messages, Setting Output Variables, Results @section Caching Results @cindex Cache To avoid checking for the same features repeatedly in various @code{configure} scripts (or repeated runs of one script), @code{configure} saves the results of many of its checks in a @dfn{cache file}. If, when a @code{configure} script runs, it finds a cache file, it reads from it the results from previous runs and avoids rerunning those checks. As a result, @code{configure} can run much faster than if it had to perform all of the checks every time. @defmac AC_CACHE_VAL (@var{cache-id}, @var{commands-to-set-it}) @maindex CACHE_VAL Ensure that the results of the check identified by @var{cache-id} are available. If the results of the check were in the cache file that was read, and @code{configure} was not given the @option{--quiet} or @option{--silent} option, print a message saying that the result was cached; otherwise, run the shell commands @var{commands-to-set-it}. If the shell commands are run to determine the value, the value will be saved in the cache file just before @code{configure} creates its output files. @xref{Cache Variable Names}, for how to choose the name of the @var{cache-id} variable. The @var{commands-to-set-it} @emph{must have no side effects} except for setting the variable @var{cache-id}, see below. @end defmac @defmac AC_CACHE_CHECK (@var{message}, @var{cache-id}, @var{commands-to-set-it}) @maindex CACHE_CHECK A wrapper for @code{AC_CACHE_VAL} that takes care of printing the messages. This macro provides a convenient shorthand for the most common way to use these macros. It calls @code{AC_MSG_CHECKING} for @var{message}, then @code{AC_CACHE_VAL} with the @var{cache-id} and @var{commands} arguments, and @code{AC_MSG_RESULT} with @var{cache-id}. The @var{commands-to-set-it} @emph{must have no side effects} except for setting the variable @var{cache-id}, see below. @end defmac It is very common to find buggy macros using @code{AC_CACHE_VAL} or @code{AC_CACHE_CHECK} because people are tempted to call @code{AC_DEFINE} in the @var{commands-to-set-it}. It is the code that follows the call to @code{AC_CACHE_VAL} should do that, based on the cached value. For instance the following macro: @example @group AC_DEFUN([AC_SHELL_TRUE], [AC_CACHE_CHECK([whether true(1) works], [ac_cv_shell_true_works], [ac_cv_shell_true_works=no true && ac_cv_shell_true_works=yes if test $ac_cv_shell_true_works = yes; then AC_DEFINE([TRUE_WORKS], 1 [Define if `true(1)' works properly.]) fi[]dnl ])]) @end group @end example @noindent is broken: if the cache is enabled, the second time this macro is run, @code{TRUE_WORKS} @emph{will not be defined}. The proper implementation is: @example @group AC_DEFUN([AC_SHELL_TRUE], [AC_CACHE_CHECK([whether true(1) works], [ac_cv_shell_true_works], [ac_cv_shell_true_works=no true && ac_cv_shell_true_works=yes]) if test $ac_cv_shell_true_works = yes; then AC_DEFINE([TRUE_WORKS], 1 [Define if `true(1)' works properly.]) fi[]dnl ]) @end group @end example Also, @var{commands-to-set-it} should not print any messages, for example with @code{AC_MSG_CHECKING}; do that before calling @code{AC_CACHE_VAL}, so the messages are printed regardless of whether the results of the check are retrieved from the cache or determined by running the shell commands. @menu * Cache Variable Names:: Shell variables used in caches * Cache Files:: Files @code{configure} uses for caching @end menu @node Cache Variable Names, Cache Files, Caching Results, Caching Results @subsection Cache Variable Names @cindex Cache variable The names of cache variables should have the following format: @example @var{package-prefix}_cv_@var{value-type}_@var{specific-value}_@ovar{additional-options} @end example @noindent for example, @samp{ac_cv_header_stat_broken} or @samp{ac_cv_prog_gcc_traditional}. The parts of the variable name are: @table @asis @item @var{package-prefix} An abbreviation for your package or organization; the same prefix you begin local Autoconf macros with, except lowercase by convention. For cache values used by the distributed Autoconf macros, this value is @samp{ac}. @item @code{_cv_} Indicates that this shell variable is a cache value. This string @emph{must} be present in the variable name, including the leading underscore. @item @var{value-type} A convention for classifying cache values, to produce a rational naming system. The values used in Autoconf are listed in @ref{Macro Names}. @item @var{specific-value} Which member of the class of cache values this test applies to. For example, which function (@samp{alloca}), program (@samp{gcc}), or output variable (@samp{INSTALL}). @item @var{additional-options} Any particular behavior of the specific member that this test applies to. For example, @samp{broken} or @samp{set}. This part of the name may be omitted if it does not apply. @end table The values assigned to cache variables may not contain newlines. Usually, their values will be boolean (@samp{yes} or @samp{no}) or the names of files or functions; so this is not an important restriction. @node Cache Files, , Cache Variable Names, Caching Results @subsection Cache Files A cache file is a shell script that caches the results of configure tests run on one system so they can be shared between configure scripts and configure runs. It is not useful on other systems. If its contents are invalid for some reason, the user may delete or edit it. By default, configure uses no cache file (technically, it uses @option{--cache-file=/dev/null}), so as to forestall problems caused by accidental use of stale cache files. To enable caching, @code{configure} accepts @option{--cache-file=@var{file}} where @var{file} is the name of the cache file to use, traditionally @file{config.cache}. The cache file is created if it does not exist already. When @code{configure} calls @code{configure} scripts in subdirectories, it uses the @option{--cache-file} argument so that they share the same cache. @xref{Subdirectories}, for information on configuring subdirectories with the @code{AC_CONFIG_SUBDIRS} macro. @file{config.status} only pays attention to the cache file if it is given the @option{--recheck} option, which makes it rerun @code{configure}. It is wrong to try to distribute cache files for particular system types. There is too much room for error in doing that, and too much administrative overhead in maintaining them. For any features that can't be guessed automatically, use the standard method of the canonical system type and linking files (@pxref{Manual Configuration}). The cache file on a particular system will gradually accumulate whenever someone runs a @code{configure} script; it will be initially nonexistent. Running @code{configure} merges the new cache results with the existing cache file. The site initialization script can specify a site-wide cache file to use instead of the default, to make it work transparently, as long as the same C compiler is used every time (@pxref{Site Defaults}). If your configure script, or a macro called from configure.in, happens to abort the configure process, it may be useful to checkpoint the cache a few times at key points using @code{AC_CACHE_SAVE}. Doing so will reduce the amount of time it takes to re-run the configure script with (hopefully) the error that caused the previous abort corrected. @c FIXME: Do we really want to document this guy? @defmac AC_CACHE_LOAD @maindex CACHE_LOAD Loads values from existing cache file, or creates a new cache file if a cache file is not found. Called automatically from @code{AC_INIT}. @end defmac @defmac AC_CACHE_SAVE @maindex CACHE_SAVE Flushes all cached values to the cache file. Called automatically from @code{AC_OUTPUT}, but it can be quite useful to call @code{AC_CACHE_SAVE} at key points in configure.in. @end defmac For instance: @example @r{ ... AC_INIT, etc. ...} @group # Checks for programs. AC_PROG_CC AC_PROG_GCC_TRADITIONAL @r{ ... more program checks ...} AC_CACHE_SAVE @end group @group # Checks for libraries. AC_CHECK_LIB(nsl, gethostbyname) AC_CHECK_LIB(socket, connect) @r{ ... more lib checks ...} AC_CACHE_SAVE @end group @group # Might abort... AM_PATH_GTK(1.0.2,, (exit 1); exit) AM_PATH_GTKMM(0.9.5,, (exit 1); exit) @end group @r{ ... AC_OUTPUT, etc. ...} @end example @node Printing Messages, , Caching Results, Results @section Printing Messages @cindex Messages, from @code{configure} @code{configure} scripts need to give users running them several kinds of information. The following macros print messages in ways appropriate for each kind. The arguments to all of them get enclosed in shell double quotes, so the shell performs variable and back quote substitution on them. These macros are all wrappers around the @code{echo} shell command. @code{configure} scripts should rarely need to run @code{echo} directly to print messages for the user. Using these macros makes it easy to change how and when each kind of message is printed; such changes need only be made to the macro definitions, and all of the callers change automatically. To diagnose static issues, i.e., when @code{autoconf} is run, see @ref{Reporting Messages}. @defmac AC_MSG_CHECKING (@var{feature-description}) @maindex MSG_CHECKING Notify the user that @code{configure} is checking for a particular feature. This macro prints a message that starts with @samp{checking } and ends with @samp{...} and no newline. It must be followed by a call to @code{AC_MSG_RESULT} to print the result of the check and the newline. The @var{feature-description} should be something like @samp{whether the Fortran compiler accepts C++ comments} or @samp{for c89}. This macro prints nothing if @code{configure} is run with the @option{--quiet} or @option{--silent} option. @end defmac @defmac AC_MSG_RESULT (@var{result-description}) @maindex MSG_RESULT Notify the user of the results of a check. @var{result-description} is almost always the value of the cache variable for the check, typically @samp{yes}, @samp{no}, or a file name. This macro should follow a call to @code{AC_MSG_CHECKING}, and the @var{result-description} should be the completion of the message printed by the call to @code{AC_MSG_CHECKING}. This macro prints nothing if @code{configure} is run with the @option{--quiet} or @option{--silent} option. @end defmac @defmac AC_MSG_NOTICE (@var{message}) @maindex MSG_NOTICE Deliver the @var{message} to the user. It is useful mainly to print a general description of the overall purpose of a group of feature checks, e.g., @example AC_MSG_NOTICE(checking if stack overflow is detectable) @end example This macro prints nothing if @code{configure} is run with the @option{--quiet} or @option{--silent} option. @end defmac @defmac AC_MSG_ERROR (@var{error-description}, @ovar{exit-status}) @maindex MSG_ERROR Notify the user of an error that prevents @code{configure} from completing. This macro prints an error message on the standard error output and exits @code{configure} with @var{exit-status} (1 by default). @var{error-description} should be something like @samp{invalid value $HOME for \$HOME}. @end defmac @defmac AC_MSG_WARN (@var{problem-description}) @maindex MSG_WARN Notify the @code{configure} user of a possible problem. This macro prints the message on the standard error output; @code{configure} continues running afterward, so macros that call @code{AC_MSG_WARN} should provide a default (back-up) behavior for the situations they warn about. @var{problem-description} should be something like @samp{ln -s seems to make hard links}. @end defmac @c ========================================================== Writing Macros. @node Writing Macros, Manual Configuration, Results, Top @chapter Writing Macros When you write a feature test that could be applicable to more than one software package, the best thing to do is encapsulate it in a new macro. Here are some instructions and guidelines for writing Autoconf macros. @menu * Macro Definitions:: Basic format of an Autoconf macro * Macro Names:: What to call your new macros * Quoting:: Protecting macros from unwanted expansion * Reporting Messages:: Notifying @code{autoconf} users * Dependencies Between Macros:: What to do when macros depend on other macros * Obsoleting Macros:: Warning about old ways of doing things * Coding Style:: Writing Autoconf macros @`a la Autoconf @end menu @node Macro Definitions, Macro Names, Writing Macros, Writing Macros @section Macro Definitions @maindex DEFUN Autoconf macros are defined using the @code{AC_DEFUN} macro, which is similar to the M4 builtin @code{define} macro. In addition to defining a macro, @code{AC_DEFUN} adds to it some code that is used to constrain the order in which macros are called (@pxref{Prerequisite Macros}). An Autoconf macro definition looks like this: @example AC_DEFUN(@var{macro-name}, @var{macro-body}) @end example You can refer to any arguments passed to the macro as @samp{$1}, @samp{$2}, etc. @xref{Definitions,, How to define new macros, m4.info, GNU m4}, for more complete information on writing M4 macros. Be sure to quote properly both the @var{macro-body} @emph{and} the @var{macro-name}, to avoid any problems if the macro happens to have been previously defined. Each macro should have a header comment that gives its prototype, and a brief description. When arguments have default values, display them in the prototype. For instance: @example # AC_MSG_ERROR(ERROR, [EXIT-STATUS = 1]) # -------------------------------------- define([AC_MSG_ERROR], [@{ _AC_ECHO([configure: error: $1], 2); exit m4_default([$2], 1); @}]) @end example Comments about the macro should be left in the header comment. Most other comments should make their way into @file{configure}, hence just keep using @samp{#} to introduce comments. @cindex @code{dnl} If you have some very special comments about pure M4 code, comments that make no sense in @file{configure} and in the header comment, then use the builtin @code{dnl}: it causes @code{m4} to discard the text through the next newline. Keep in mind that @code{dnl} is rarely needed to introduce comments, rather it is useful to get rid of the newlines following macros that produce no output, such as @code{AC_REQUIRE}. @node Macro Names, Quoting, Macro Definitions, Writing Macros @section Macro Names All of the Autoconf macros have all-uppercase names starting with @samp{AC_} to prevent them from accidentally conflicting with other text. All shell variables that they use for internal purposes have mostly-lowercase names starting with @samp{ac_}. To ensure that your macros don't conflict with present or future Autoconf macros, you should prefix your own macro names and any shell variables they use with some other sequence. Possibilities include your initials, or an abbreviation for the name of your organization or software package. Most of the Autoconf macros' names follow a structured naming convention that indicates the kind of feature check by the name. The macro names consist of several words, separated by underscores, going from most general to most specific. The names of their cache variables use the same convention (@pxref{Cache Variable Names}, for more information on them). The first word of the name after @samp{AC_} usually tells the category of feature being tested. Here are the categories used in Autoconf for specific test macros, the kind of macro that you are more likely to write. They are also used for cache variables, in all-lowercase. Use them where applicable; where they're not, invent your own categories. @table @code @item C C language builtin features. @item DECL Declarations of C variables in header files. @item FUNC Functions in libraries. @item GROUP @sc{unix} group owners of files. @item HEADER Header files. @item LIB C libraries. @item PATH The full path names to files, including programs. @item PROG The base names of programs. @item MEMBER Members of aggregates. @item SYS Operating system features. @item TYPE C builtin or declared types. @item VAR C variables in libraries. @end table After the category comes the name of the particular feature being tested. Any further words in the macro name indicate particular aspects of the feature. For example, @code{AC_FUNC_UTIME_NULL} checks the behavior of the @code{utime} function when called with a @code{NULL} pointer. An internal macro should have a name that starts with an underscore; Autoconf internals should therefore start with @samp{_AC_}. Additionally, a macro that is an internal subroutine of another macro should have a name that starts with an underscore and the name of that other macro, followed by one or more words saying what the internal macro does. For example, @code{AC_PATH_X} has internal macros @code{_AC_PATH_X_XMKMF} and @code{_AC_PATH_X_DIRECT}. @node Quoting, Reporting Messages, Macro Names, Writing Macros @section Quoting @cindex quotation @c FIXME: Grmph, yet another quoting myth: quotation has *never* @c prevented `expansion' of $1. Unless it refers to the expansion @c of the value of $1? Anyway, we need a rewrite here... The most common brokenness of existing macros is an improper quotation. This section, which users of Autoconf can skip, but which macro writers @emph{must} read, first justifies the quotation scheme that was chosen for Autoconf, and ends with the rule of thumb. Understanding the former helps following the latter. @menu * Active Characters:: Characters that change the behavior of m4 * One Macro Call:: Quotation and one macro call * Quotation and Nested Macros:: Macros calling macros * Quotation Rule Of Thumb:: One parenthesis, one quote @end menu @node Active Characters, One Macro Call, Quoting, Quoting @subsection Active Characters To fully understand where proper quotation is precious, you first need to know what are the special characters in Autoconf: @samp{#} introduces a comment inside which no macro expansion is performed, @samp{,} separates arguments, @samp{[} and @samp{]} are the quotes themselves, and finally @samp{(} and @samp{)} which @code{m4} tries to match by pairs. In order to understand the delicate case of macro calls, we first have to present some obvious failures. Below they are ``obviousified'', although you find them in real life, they are usually in disguise. Comments, introduced by a hash and running up to the newline, are opaque tokens to the top level: active characters are turned off, and there is no macro expansion: @example # define([def], ine) @result{}# define([def], ine) @end example Each time there can be a macro expansion, there is a quotation expansion, i.e., one level of quotes is stripped: @example int tab[10]; @result{}int tab10; [int tab[10];] @result{}int tab[10]; @end example Without this in mind, the reader will hopelessly try to find a means to use her macro @code{array}: @example define([array], [int tab[10];]) array @result{}int tab10; [array] @result{}array @end example @noindent How can you correctly output the intended results@footnote{Using @code{defn}.}? @node One Macro Call, Quotation and Nested Macros, Active Characters, Quoting @subsection One Macro Call Let's proceed on the interaction between active characters and macros with this small macro which just returns its first argument: @example define([car], [$1]) @end example @noindent The two pairs of quotes above are not part of the arguments of @code{define}, rather, they are understood by the top level when it tries to find the arguments of @code{define}, therefore it is equivalent to write: @example define(car, $1) @end example @noindent But, while it is acceptable for a @file{configure.in} to avoid unneeded quotes, it is bad practice for Autoconf macros which must both be more robust, and advocate the perfect writing. At the top level, there are only two possible quoting: either you quote, or you don't: @example car(foo, bar, baz) @result{}foo [car(foo, bar, baz)] @result{}car(foo, bar, baz) @end example Let's pay attention to the special characters: @example car(#) @error{}EOF in argument list @end example The closing parenthesis is hidden in the comment; with a hypothetical quoting, the top level understood this: @example car([#)] @end example @noindent Proper quotation, of course, fixes the problem: @example car([#]) @result{}# @end example The reader will easily understand the following examples: @example car(foo, bar) @result{}foo car([foo, bar]) @result{}foo, bar car((foo, bar)) @result{}(foo, bar) car([(foo], [bar)]) @result{}(foo car([], []) @result{} car([[]], [[]]) @result{}[] @end example With this in mind, we can explore the cases where macros invoke macros... @node Quotation and Nested Macros, Quotation Rule Of Thumb, One Macro Call, Quoting @subsection Quotation and Nested Macros The examples below use the following macros: @example define([car], [$1]) define([active], [ACT, IVE]) define([array], [int tab[10]]) @end example Each additional embedded macro call introduces other possible interesting quotations: @example car(active) @result{}ACT car([active]) @result{}ACT, IVE car([[active]]) @result{}active @end example In the first case, the top level looks for the arguments of @code{car}, and finds @samp{active}. Because @code{m4} evaluates its arguments before applying the macro, @samp{active} is expanded, which results in @example car(ACT, IVE) @result{}ACT @end example @noindent In the second case, the top level gives @samp{active} as first and only argument of @code{car}, which results in @example active @result{}ACT, IVE @end example @noindent i.e., the argument is evaluated @emph{after} the macro that invokes it. In the third case, @code{car} receives @samp{[active]}, which results in @example [active] @result{}active @end example @noindent exactly as we already saw above. The example above, applied to a more realistic example, gives: @example car(int tab[10];) @result{}int tab10; car([int tab[10];]) @result{}int tab10; car([[int tab[10];]]) @result{}int tab[10]; @end example @noindent Huh? The first case is easily understood, but why is the second wrong, and the third right? To understand that, you must know that after @code{m4} expands a macro the resulting text is immediately subjected to macro expansion and quote removal. This means that the quote removal occurs twice - first time before the argument is passed to the @code{car} macro, and the second time after the @code{car} macro expands to the first argument. As the author of the Autoconf macro @code{car} you then consider it is incorrect to require that your users have to double quote the arguments of @code{car}, so you ``fix'' your macro. Let's call it @code{qar} for quoted car: @example define([qar], [[$1]]) @end example @noindent and check that @code{qar} is properly fixed: @example qar([int tab[10];]) @result{}int tab[10]; @end example @noindent Ahhh! That's much better. But note what you've done: now that the arguments are literal strings, if the user wants to use the results of expansions as arguments, she has to leave an @emph{unquoted} macro call: @example qar(active) @result{}ACT @end example @noindent while she wanted to reproduce what she used to do with @code{car}: @example car([active]) @result{}ACT, IVE @end example @noindent Worse yet: she wants to use a macro that produces a set of @code{cpp} macros: @example define([my_includes], [#include ]) car([my_includes]) @result{}#include qar(my_includes) @error{}EOF in argument list @end example This macro, @code{qar}, because it double quotes its arguments, forces its users to leave their macro calls unquoted, which is dangerous. Commas and other active symbols are interpreted by @code{m4} before they are given to the macro, often not in the way the users expect. Also, because @code{qar} behaves differently from the other macros, it's an exception that should be avoided in Autoconf. @node Quotation Rule Of Thumb, , Quotation and Nested Macros, Quoting @subsection Quotation Rule Of Thumb To conclude, the quotation rule of thumb is: @center @emph{One pair of quotes per pair of parentheses.} Never over-quote, never under-quote, in particular in the definition of macros. In the few places where the macros need to use brackets (usually in C program text or regular expressions), quote properly @emph{the arguments}! It is frequent to read Autoconf programs with snippets like: @example AC_TRY_LINK( changequote(<<, >>)dnl <<#include #ifndef tzname /* For SGI. */ extern char *tzname[]; /* RS6000 and others reject char **tzname. */ #endif>>, changequote([, ])dnl [atoi (*tzname);], ac_cv_var_tzname=yes, ac_cv_var_tzname=no) @end example @noindent which is incredibly useless since @code{AC_TRY_LINK} is @emph{already} double quoting, so you just need: @example AC_TRY_LINK( [#include #ifndef tzname /* For SGI. */ extern char *tzname[]; /* RS6000 and others reject char **tzname. */ #endif], [atoi (*tzname);], [ac_cv_var_tzname=yes], [ac_cv_var_tzname=no]) @end example @noindent The M4 fluent reader noted that these two writings are rigorously equivalent, since @code{m4} swallows both the @samp{changequote(<<, >>)} and @samp{<<} @samp{>>} when it @dfn{collects} the arguments: these quotes are not part of the arguments! Simplified, the example above is just doing this: @example changequote(<<, >>)dnl <<[]>> changequote([, ])dnl @end example @noindent instead of simply @example [[]] @end example With macros which do not double quote their arguments (which is the rule), double quote the (risky) literals: @example AC_LINK_IFELSE([AC_LANG_PROGRAM( [[#include #ifndef tzname /* For SGI. */ extern char *tzname[]; /* RS6000 and others reject char **tzname. */ #endif]], [atoi (*tzname);])], [ac_cv_var_tzname=yes], [ac_cv_var_tzname=no]) @end example @c FIXME: Quadrigraphs and hopeless cases. When you create a @code{configure} script using newly written macros, examine it carefully to check whether you need to add more quotes in your macros. If one or more words have disappeared in the @code{m4} output, you need more quotes. When in doubt, quote. However, it's also possible to put on too many layers of quotes. If this happens, the resulting @code{configure} script will contain unexpanded macros. The @code{autoconf} program checks for this problem by doing @samp{grep AC_ configure}. @node Reporting Messages, Dependencies Between Macros, Quoting, Writing Macros @section Reporting Messages @cindex Messages, from @code{autoconf} When macros statically diagnose abnormal situations, benign or fatal, they should report them using these macros. For dynamic issues, i.e., when @code{configure} is run, see @ref{Printing Messages}. @defmac AC_DIAGNOSE (@var{category}, @var{message}) @maindex DIAGNOSE Report @var{message} as a warning (or as an error if requested by the user) if it falls into the @var{category}. You are encouraged to use standard categories, which currently include: @table @samp @item all messages that don't fall into one of the following category. Use of an empty @var{category} is equivalent. @item cross related to cross compilation issues. @item obsolete use of an obsolete construct. @item syntax dubious syntactic constructs, incorrectly ordered macro calls. @end table @end defmac @defmac AC_WARNING (@var{message}) @maindex WARNING Equivalent to @samp{AC_DIAGNOSE([syntax], @var{message})}, but you are strongly encouraged to use a finer grained category. @end defmac @defmac AC_FATAL (@var{message}) @maindex FATAL Report a severe error @var{message}, and have @code{autoconf} die. @end defmac When the user runs @samp{autoconf -W error}, warnings from @code{AC_DIAGNOSE} and @code{AC_WARNING} are reported as error, see @ref{autoconf Invocation}. @node Dependencies Between Macros, Obsoleting Macros, Reporting Messages, Writing Macros @section Dependencies Between Macros Some Autoconf macros depend on other macros having been called first in order to work correctly. Autoconf provides a way to ensure that certain macros are called if needed and a way to warn the user if macros are called in an order that might cause incorrect operation. @menu * Prerequisite Macros:: Ensuring required information * Suggested Ordering:: Warning about possible ordering problems @end menu @node Prerequisite Macros, Suggested Ordering, Dependencies Between Macros, Dependencies Between Macros @subsection Prerequisite Macros A macro that you write might need to use values that have previously been computed by other macros. For example, @code{AC_DECL_YYTEXT} examines the output of @code{flex} or @code{lex}, so it depends on @code{AC_PROG_LEX} having been called first to set the shell variable @code{LEX}. Rather than forcing the user of the macros to keep track of the dependencies between them, you can use the @code{AC_REQUIRE} macro to do it automatically. @code{AC_REQUIRE} can ensure that a macro is only called if it is needed, and only called once. @defmac AC_REQUIRE (@var{macro-name}) @maindex REQUIRE If the M4 macro @var{macro-name} has not already been called, call it (without any arguments). Make sure to quote @var{macro-name} with square brackets. @var{macro-name} must have been defined using @code{AC_DEFUN} or else contain a call to @code{AC_PROVIDE} to indicate that it has been called. @code{AC_REQUIRE} must be used inside an @code{AC_DEFUN}'d macro, it must not be called from the top level. @end defmac @code{AC_REQUIRE} is often misunderstood, it really implements dependencies between macros in the sense that if a macro depends upon another, the latter will be expanded @emph{before} the body of the former. In particular, @samp{AC_REQUIRE(FOO)} is not replaced with the body of @code{FOO}. For instance, this definition of macros @example @group AC_DEFUN([TRAVOLTA], [test "$body_temparature_in_celsius" -gt "38" && dance_floor=occupied]) AC_DEFUN([NEWTON_JOHN], [test "$hair_style" = "curly" && dance_floor=occupied]) @end group @group AC_DEFUN([RESERVE_DANCE_FLOOR], [if date | grep '^Sat.*pm' >/dev/null 2>&1; then AC_REQUIRE([TRAVOLTA]) AC_REQUIRE([NEWTON_JOHN]) fi]) @end group @end example @noindent with this @file{configure.in} @example AC_INIT RESERVE_DANCE_FLOOR if test "$dance_floor" = occupied; then AC_MSG_ERROR([cannot pick up here, let's move]) fi @end example @noindent will not leave you with a better chance to meet the kindred soul the other times that the Saturday night since it expands into: @example @group test "$body_temperature_in_Celsius" -gt "38" && dance_floor=occupied test "$hair_style" = "curly" && dance_floor=occupied fi if date | grep '^Sat.*pm' >/dev/null 2>&1; then fi @end group @end example This behavior was chosen on purpose: (i) it avoids that messages from required macros interrupt the messages from the requiring macros, (ii), it avoids bad surprises when shell conditionals are used, as in: @example @group if ...; then AC_REQUIRE([SOME_CHECK]) fi ... SOME_CHECK @end group @end example You are encouraged to put all the @code{AC_REQUIRE}s at the beginning of the macros. You can use @code{dnl} to avoid the empty line they leave. @node Suggested Ordering, , Prerequisite Macros, Dependencies Between Macros @subsection Suggested Ordering Some macros should be run before another macro if both are called, but neither @emph{requires} that the other be called. For example, a macro that changes the behavior of the C compiler should be called before any macros that run the C compiler. Many of these dependencies are noted in the documentation. Autoconf provides the @code{AC_BEFORE} macro to warn users when macros with this kind of dependency appear out of order in a @file{configure.in} file. The warning occurs when creating @code{configure} from @file{configure.in}, not when running @code{configure}. For example, @code{AC_PROG_CPP} checks whether the C compiler can run the C preprocessor when given the @option{-E} option. It should therefore be called after any macros that change which C compiler is being used, such as @code{AC_PROG_CC}. So @code{AC_PROG_CC} contains: @example AC_BEFORE([$0], [AC_PROG_CPP])dnl @end example @noindent This warns the user if a call to @code{AC_PROG_CPP} has already occurred when @code{AC_PROG_CC} is called. @defmac AC_BEFORE (@var{this-macro-name}, @var{called-macro-name}) @maindex BEFORE Make @code{m4} print a warning message on the standard error output if @var{called-macro-name} has already been called. @var{this-macro-name} should be the name of the macro that is calling @code{AC_BEFORE}. The macro @var{called-macro-name} must have been defined using @code{AC_DEFUN} or else contain a call to @code{AC_PROVIDE} to indicate that it has been called. @end defmac @node Obsoleting Macros, Coding Style, Dependencies Between Macros, Writing Macros @section Obsoleting Macros Configuration and portability technology has evolved over the years. Often better ways of solving a particular problem are developed, or ad-hoc approaches are systematized. This process has occurred in many parts of Autoconf. One result is that some of the macros are now considered @dfn{obsolete}; they still work, but are no longer considered the best thing to do, hence they should be replaced with more modern macros. Ideally, @code{autoupdate} should substitute the old macro calls with their modern implementation. Autoconf provides a simple means to obsolete a macro. @defmac AU_DEFUN (@var{old-macro}, @var{implementation}, @ovar{message}) @maindex DEFUN @maindex AU_DEFUN Define @var{old-macro} as @var{implementation}. The only difference with @code{AC_DEFUN} is that the user will be warned that @var{old-macro} is now obsolete. If she then uses @code{autoupdate}, the call to @var{old-macro} will be replaced by the modern @var{implementation}. The additional @var{message} is then printed. @end defmac @node Coding Style, , Obsoleting Macros, Writing Macros @section Coding Style The Autoconf macros follow a strict coding style. You are encouraged to follow this style, especially if you intend to distribute your macro, either by contributing it to Autoconf itself, or via other means. The first requirement is to pay great attention to the quotation, for more details, see @ref{Autoconf Language}, and @ref{Quoting}. Do not try to invent new interfaces, it is likely that there is a macro in Autoconf that resembles the macro you are defining: try to stick to this existing interface (order of arguments, default values etc.). We @emph{are} conscious that some of these interfaces are not perfect, nevertheless, when harmless, homogeneity should be preferred over creativity. Be careful about clashes both between M4 symbols, and shell variables. If you stick to the suggested M4 naming scheme (@pxref{Macro Names}) you are unlikely to generate conflicts. Nevertheless, when you need to set a special value, @emph{avoid using a regular macro name}, rather, use an ``impossible'' name. For instance, up to version 2.13, the macro @code{AC_SUBST} used to remember what @var{symbol}s were already defined by setting @code{AC_SUBST_@var{symbol}}, which is a regular macro name. But since there is a macro named @code{AC_SUBST_FILE} it was just impossible to @samp{AC_SUBST(FILE)}! In this case, @code{AC_SUBST(@var{symbol})} or @code{_AC_SUBST(@var{symbol})} should have been used (yes, with the parentheses). Or better yet, using high level macros such as @code{AC_EXPAND_ONCE}. No Autoconf macro should ever enter the user variables name space, i.e., but the variables that are the actual result of running the macro, all the shell variables should start with @code{ac_}. In addition, small macros or any macro that is likely to be embedded in other macros should be careful not to use obvious names. @cindex @code{dnl} Do not use @code{dnl} to introduce comments: most of the comments you are likely to write are either header comments which are not output anyway, or comments that should make their way into @file{configure}. There are exceptional cases where you do want to comment special M4 constructs, in which case @code{dnl} is right, but keep in mind that it is unlikely. M4 ignores the leading spaces before each argument, use this feature to indent in such a way that arguments are (more or less) aligned with the opening parenthesis of the macro being called. For instance, instead of @example AC_CACHE_CHECK(for EMX OS/2 environment, ac_cv_emxos2, [AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, [return __EMX__;])], [ac_cv_emxos2=yes], [ac_cv_emxos2=no])]) @end example @noindent write @example AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2], [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])], [ac_cv_emxos2=yes], [ac_cv_emxos2=no])]) @end example @noindent or even @example AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2], [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])], [ac_cv_emxos2=yes], [ac_cv_emxos2=no])]) @end example When using @code{AC_TRY_RUN} or any macro that cannot work when cross-compiling, provide a pessimistic value (typically @samp{no}). Feel free to use various tricks to avoid that auxiliary tools, such as syntax-highlighting editors, behave improperly. For instance, instead of @example patsubst([$1], [$"]) @end example @noindent use @example patsubst([$1], [$""]) @end example @noindent so that Emacsen do not open a endless ``string'' at the first quote. For the same reasons, avoid @example test $[#] != 0 @end example @noindent but use @example test $[@@%:@@] != 0 @end example @noindent otherwise, the closing bracket would be hidden inside a @samp{#}-comment breaking the bracket matching highlighting from Emacsen. Note the preferred style to escape from M4: @samp{$[1]}, @samp{$[@@]} etc. Do not escape when it is unneeded. Common examples of useless quotation are @samp{[$]$1} (write @samp{$$1}), @samp{[$]var} (use @samp{$var}), etc. If you add portability issues to the picture, you'll prefer @samp{$@{1+"$[@@]"@}} to @samp{"[$]@@"}, and you'll prefer do something better than hacking Autoconf @code{:-)}. When using @command{sed}, don't use @option{-e} but for indenting purpose. With the @code{s} command, the preferred separator is @samp{/} unless @samp{/} itself is used in the command, in which case you should use @samp{,}. @xref{Macro Definitions}, for details on how to define a macro. If a macro doesn't use @code{AC_REQUIRE} and it is expected never to be the object of an @code{AC_REQUIRE} directive, then use @code{define}. In case of doubt, use @code{AC_DEFUN}. All the @code{AC_REQUIRE} statements should be at the beginning of the macro, @code{dnl}'ed. You should not rely on the number of arguments: instead of checking whether an argument is missing, test that it is not empty. It both provides a simpler and more predictable interface to the user, and saves room for further arguments. Unless the macro is short, try to leave the closing @samp{])} at the beginning of a line, followed by a comment that repeats the name of the macro being defined. If you want to avoid the new-line which is then introduced, use @code{dnl}. Better yet, use @samp{[]dnl} @emph{even} behind of parenthesis, since because of the M4 evaluation rule the @samp{dnl} might be appended to the result of the evaluation of the macro before it (e.g., leading to @samp{yesdnl} instead of @samp{yes}). For instance, instead of: @example AC_DEFUN([AC_PATH_X], [AC_MSG_CHECKING(for X) AC_REQUIRE_CPP() @r{# cut...} AC_MSG_RESULT([libraries $x_libraries, headers $x_includes]) fi]) @end example @noindent write: @example AC_DEFUN([AC_PATH_X], [AC_REQUIRE_CPP()dnl AC_MSG_CHECKING(for X) @r{# cut...} AC_MSG_RESULT([libraries $x_libraries, headers $x_includes]) fi[]dnl ])# AC_PATH_X @end example If the macro is long, try to split it into logical chunks. Typically, macros that check for a bug in a function and prepare its @code{AC_LIBOBJ} replacement should have an auxiliary macro to perform this setup. Do not hesitate to introduce auxiliary macros to factor your code. In order to highlight this coding style, here is a macro written the old way: @example dnl Check for EMX on OS/2. dnl _AC_EMXOS2 AC_DEFUN(_AC_EMXOS2, [AC_CACHE_CHECK(for EMX OS/2 environment, ac_cv_emxos2, [AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, return __EMX__;)], ac_cv_emxos2=yes, ac_cv_emxos2=no)]) test "$ac_cv_emxos2" = yes && EMXOS2=yes]) @end example @noindent and the new way: @example # _AC_EMXOS2 # ---------- # Check for EMX on OS/2. define([_AC_EMXOS2], [AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2], [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])], [ac_cv_emxos2=yes], [ac_cv_emxos2=no])]) test "$ac_cv_emxos2" = yes && EMXOS2=yes[]dnl ])# _AC_EMXOS2 @end example @c ================================================== Manual Configuration @node Manual Configuration, Site Configuration, Writing Macros, Top @chapter Manual Configuration A few kinds of features can't be guessed automatically by running test programs. For example, the details of the object file format, or special options that need to be passed to the compiler or linker. You can check for such features using ad-hoc means, such as having @code{configure} check the output of the @code{uname} program, or looking for libraries that are unique to particular systems. However, Autoconf provides a uniform method for handling unguessable features. @menu * Specifying Names:: Specifying the system type * Canonicalizing:: Getting the canonical system type * Using System Type:: What to do with the system type @end menu @node Specifying Names, Canonicalizing, Manual Configuration, Manual Configuration @section Specifying the System Type Like other @sc{gnu} @code{configure} scripts, Autoconf-generated @code{configure} scripts can make decisions based on a canonical name for the system type, which has the form @samp{@var{cpu}-@var{vendor}-@var{os}}, where @var{os} can be @samp{@var{system}} or @samp{@var{kernel}-@var{system}} @code{configure} can usually guess the canonical name for the type of system it's running on. To do so it runs a script called @code{config.guess}, which derives the name using the @code{uname} command or symbols predefined by the C preprocessor. Alternately, the user can specify the system type with command line arguments to @code{configure}. Doing so is necessary when cross-compiling. In the most complex case of cross-compiling, three system types are involved. The options to specify them are@footnote{For backward compatibility, @code{configure} will accept a system type as an option by itself. Such an option will override the defaults for build, host and target system types. The following configure statement will configure a cross toolchain that will run on NetBSD/alpha but generate code for GNU Hurd/sparc, which is also the build platform. @example ./configure --host=alpha-netbsd sparc-gnu @end example }: @table @option @item --build=@var{build-type} the type of system on which the package is being configured and compiled. @item --host=@var{host-type} @ovindex cross_compiling the type of system on which the package will run. @item --target=@var{target-type} the type of system for which any compiler tools in the package will produce code (rarely needed). By default, it is the same as host. @end table They all default to the result of running @code{config.guess}, unless you specify either @samp{--build} or @samp{--host}. In this case, the default becomes the system type you specified. If you specify both, and they're different, @code{configure} will enter cross compilation mode, so it won't run any tests that require execution. Hint: if you mean to override the result of @code{config.guess}, prefer @samp{--build} over @samp{--host}. In the future, @samp{--host} will not override the name of the build system type. Also, when you specify @samp{--host}, but not @samp{--build}, when @code{configure} performs the first compiler test, it will try to run an executable produced by the compiler. If the execution fails, it will enter cross compilation mode. Note, however, that it won't guess the build system type, since this may require running test programs. Moreover, by the time the compiler test is performed, it may be too late to modify the build system type: other tests may have already been performed. Therefore, whenever you specify @code{--host}, be sure to specify @code{--build} too. @example ./configure --build=i686-pc-linux-gnu --host=m68k-coff @end example @noindent will enter cross compilation mode, but @code{configure} will fail if it can't run the code generated by the specified compiler if you configure as follows: @example ./configure CC=m68k-coff-gcc @end example @code{configure} recognizes short aliases for many system types; for example, @samp{decstation} can be used instead of @samp{mips-dec-ultrix4.2}. @code{configure} runs a script called @code{config.sub} to canonicalize system type aliases. @node Canonicalizing, Using System Type, Specifying Names, Manual Configuration @section Getting the Canonical System Type The following macros make the system type available to @code{configure} scripts. @ovindex build_alias @ovindex host_alias @ovindex target_alias The variables @samp{build_alias}, @samp{host_alias}, and @samp{target_alias} are always exactly the arguments of @samp{--build}, @samp{--host}, and @samp{--target}, in particular they are left empty if the user did not use them, even if the corresponding @code{AC_CANONICAL} macro was run. Any configure script may use these variables anywhere. These are the variables that should be used when in interaction with the user. If you need to recognize some special environments based on their system type, run the following macros to get canonical system names. These variables are not set before the macro call. If you use these macros, you must distribute @code{config.guess} and @code{config.sub} along with your source code. @xref{Output}, for information about the @code{AC_CONFIG_AUX_DIR} macro which you can use to control in which directory @code{configure} looks for those scripts. @defmac AC_CANONICAL_BUILD @maindex CANONICAL_BUILD @ovindex build @ovindex build_cpu @ovindex build_vendor @ovindex build_os Compute the canonical build system type variable, @code{build}, and its three individual parts @code{build_cpu}, @code{build_vendor}, and @code{build_os}. If @samp{--build} was specified, then @code{build} is the canonicalization of @code{build_alias} by @command{config.sub}, otherwise it is determined by the shell script @code{config.guess}. @end defmac @defmac AC_CANONICAL_HOST @maindex CANONICAL_HOST @ovindex host @ovindex host_cpu @ovindex host_vendor @ovindex host_os Compute the canonical host system type variable, @code{host}, and its three individual parts @code{host_cpu}, @code{host_vendor}, and @code{host_os}. If @samp{--host} was specified, then @code{host} is the canonicalization of @code{host_alias} by @command{config.sub}, otherwise it defaults to @code{build}. For temporary backward-compatibility, when @samp{--host} is specified by @samp{--build} isn't, the build system will be assumed to be the same as @samp{--host}, and @samp{build_alias} will be set to that value. Eventually, this historically incorrect behavior will go away. @end defmac @defmac AC_CANONICAL_TARGET @maindex CANONICAL_TARGET @ovindex target @ovindex target_cpu @ovindex target_vendor @ovindex target_os Compute the canonical target system type variable, @code{target}, and its three individual parts @code{target_cpu}, @code{target_vendor}, and @code{target_os}. If @samp{--target} was specified, then @code{target} is the canonicalization of @code{target_alias} by @command{config.sub}, otherwise it defaults to @code{host}. @end defmac @node Using System Type, , Canonicalizing, Manual Configuration @section Using the System Type How do you use a canonical system type? Usually, you use it in one or more @code{case} statements in @file{configure.in} to select system-specific C files. Then, using @code{AC_CONFIG_LINKS}, link those files which have names based on the system name, to generic names, such as @file{host.h} or @file{target.c} (@pxref{Configuration Links}). The @code{case} statement patterns can use shell wild cards to group several cases together, like in this fragment: @example case "$target" in i386-*-mach* | i386-*-gnu*) obj_format=aout emulation=mach bfd_gas=yes ;; i960-*-bout) obj_format=bout ;; esac @end example @noindent and in @file{configure.in}, use: @example AC_CONFIG_LINKS(host.h:config/$machine.h object.h:config/$obj_format.h) @end example You can also use the host system type to find cross-compilation tools. @xref{Generic Programs}, for information about the @code{AC_CHECK_TOOL} macro which does that. @c ===================================================== Site Configuration. @node Site Configuration, Running configure scripts, Manual Configuration, Top @chapter Site Configuration @code{configure} scripts support several kinds of local configuration decisions. There are ways for users to specify where external software packages are, include or exclude optional features, install programs under modified names, and set default values for @code{configure} options. @menu * External Software:: Working with other optional software * Package Options:: Selecting optional features * Pretty Help Strings:: Formating help string * Site Details:: Configuring site details * Transforming Names:: Changing program names when installing * Site Defaults:: Giving @code{configure} local defaults @end menu @node External Software, Package Options, Site Configuration, Site Configuration @section Working With External Software Some packages require, or can optionally use, other software packages that are already installed. The user can give @code{configure} command line options to specify which such external software to use. The options have one of these forms: @example --with-@var{package}=@ovar{arg} --without-@var{package} @end example For example, @option{--with-gnu-ld} means work with the @sc{gnu} linker instead of some other linker. @option{--with-x} means work with The X Window System. The user can give an argument by following the package name with @samp{=} and the argument. Giving an argument of @samp{no} is for packages that are used by default; it says to @emph{not} use the package. An argument that is neither @samp{yes} nor @samp{no} could include a name or number of a version of the other package, to specify more precisely which other package this program is supposed to work with. If no argument is given, it defaults to @samp{yes}. @option{--without-@var{package}} is equivalent to @option{--with-@var{package}=no}. @code{configure} scripts do not complain about @option{--with-@var{package}} options that they do not support. This behavior permits configuring a source tree containing multiple packages with a top-level @code{configure} script when the packages support different options, without spurious error messages about options that some of the packages support. An unfortunate side effect is that option spelling errors are not diagnosed. No better approach to this problem has been suggested so far. For each external software package that may be used, @file{configure.in} should call @code{AC_ARG_WITH} to detect whether the @code{configure} user asked to use it. Whether each package is used or not by default, and which arguments are valid, is up to you. @defmac AC_ARG_WITH (@var{package}, @var{help-string}, @ovar{action-if-given}, @ovar{action-if-not-given}) @maindex ARG_WITH If the user gave @code{configure} the option @option{--with-@var{package}} or @option{--without-@var{package}}, run shell commands @var{action-if-given}. If neither option was given, run shell commands @var{action-if-not-given}. The name @var{package} indicates another software package that this program should work with. It should consist only of alphanumeric characters and dashes. The option's argument is available to the shell commands @var{action-if-given} in the shell variable @code{withval}, which is actually just the value of the shell variable @code{with_@var{package}}, with any @option{-} characters changed into @samp{_}. You may use that variable instead, if you wish. The argument @var{help-string} is a description of the option which looks like this: @example --with-readline support fancy command line editing @end example @noindent @var{help-string} may be more than one line long, if more detail is needed. Just make sure the columns line up in @samp{configure --help}. Avoid tabs in the help string. You'll need to enclose it in @samp{[} and @samp{]} in order to produce the leading spaces. You should format your @var{help-string} with the macro @code{AC_HELP_STRING} (@pxref{Pretty Help Strings}). @end defmac @defmac AC_WITH (@var{package}, @var{action-if-given}, @ovar{action-if-not-given}) @maindex WITH This is an obsolete version of @code{AC_ARG_WITH} that does not support providing a help string. @end defmac @node Package Options, Pretty Help Strings, External Software, Site Configuration @section Choosing Package Options If a software package has optional compile-time features, the user can give @code{configure} command line options to specify whether to compile them. The options have one of these forms: @example --enable-@var{feature}=@ovar{arg} --disable-@var{feature} @end example These options allow users to choose which optional features to build and install. @option{--enable-@var{feature}} options should never make a feature behave differently or cause one feature to replace another. They should only cause parts of the program to be built rather than left out. The user can give an argument by following the feature name with @samp{=} and the argument. Giving an argument of @samp{no} requests that the feature @emph{not} be made available. A feature with an argument looks like @option{--enable-debug=stabs}. If no argument is given, it defaults to @samp{yes}. @option{--disable-@var{feature}} is equivalent to @option{--enable-@var{feature}=no}. @code{configure} scripts do not complain about @option{--enable-@var{feature}} options that they do not support. This behavior permits configuring a source tree containing multiple packages with a top-level @code{configure} script when the packages support different options, without spurious error messages about options that some of the packages support. An unfortunate side effect is that option spelling errors are not diagnosed. No better approach to this problem has been suggested so far. For each optional feature, @file{configure.in} should call @code{AC_ARG_ENABLE} to detect whether the @code{configure} user asked to include it. Whether each feature is included or not by default, and which arguments are valid, is up to you. @defmac AC_ARG_ENABLE (@var{feature}, @var{help-string}, @ovar{action-if-given}, @ovar{action-if-not-given}) @maindex ARG_ENABLE If the user gave @code{configure} the option @option{--enable-@var{feature}} or @option{--disable-@var{feature}}, run shell commands @var{action-if-given}. If neither option was given, run shell commands @var{action-if-not-given}. The name @var{feature} indicates an optional user-level facility. It should consist only of alphanumeric characters and dashes. The option's argument is available to the shell commands @var{action-if-given} in the shell variable @code{enableval}, which is actually just the value of the shell variable @code{enable_@var{feature}}, with any @option{-} characters changed into @samp{_}. You may use that variable instead, if you wish. The @var{help-string} argument is like that of @code{AC_ARG_WITH} (@pxref{External Software}). You should format your @var{help-string} with the macro @code{AC_HELP_STRING} (@pxref{Pretty Help Strings}). @end defmac @defmac AC_ENABLE (@var{feature}, @var{action-if-given}, @ovar{action-if-not-given}) @maindex ENABLE This is an obsolete version of @code{AC_ARG_ENABLE} that does not support providing a help string. @end defmac @node Pretty Help Strings, Site Details, Package Options, Site Configuration @section Making Your Help Strings Look Pretty Properly formatting the @samp{help strings} which are used in @code{AC_ARG_WITH} (@pxref{External Software}) and @code{AC_ARG_ENABLE} (@pxref{Package Options}) can be challenging. Specifically, you want your own @samp{help strings} to line up in the appropriate columns of @samp{configure --help} just like the standard Autoconf @samp{help strings} do. This is the purpose of the @code{AC_HELP_STRING} macro. @defmac AC_HELP_STRING (@var{left-hand-side}, @var{right-hand-side}) @maindex HELP_STRING Expands into an help string that looks pretty when the user executes @samp{configure --help}. It is typically used in @code{AC_ARG_WITH} (@pxref{External Software}) or @code{AC_ARG_ENABLE} (@pxref{Package Options}). The following example will make this clearer. @example AC_DEFUN(TEST_MACRO, [AC_ARG_WITH(foo, AC_HELP_STRING([--with-foo], [use foo (default is NO)]), ac_cv_use_foo=$withval, ac_cv_use_foo=no), AC_CACHE_CHECK(whether to use foo, ac_cv_use_foo, ac_cv_use_foo=no)]) @end example Please note that the call to @code{AC_HELP_STRING} is @strong{unquoted}. Then the last few lines of @samp{configure --help} will appear like this: @example --enable and --with options recognized: --with-foo use foo (default is NO) @end example The @code{AC_HELP_STRING} macro is particularly helpful when the @var{left-hand-side} and/or @var{right-hand-side} are composed of macro arguments, as shown in the following example. @example AC_DEFUN(MY_ARG_WITH, [AC_ARG_WITH([$1], AC_HELP_STRING([--with-$1], [use $1 (default is $2)]), ac_cv_use_$1=$withval, ac_cv_use_$1=no), AC_CACHE_CHECK(whether to use $1, ac_cv_use_$1, ac_cv_use_$1=$2)]) @end example @end defmac @node Site Details, Transforming Names, Pretty Help Strings, Site Configuration @section Configuring Site Details Some software packages require complex site-specific information. Some examples are host names to use for certain services, company names, and email addresses to contact. Since some configuration scripts generated by Metaconfig ask for such information interactively, people sometimes wonder how to get that information in Autoconf-generated configuration scripts, which aren't interactive. Such site configuration information should be put in a file that is edited @emph{only by users}, not by programs. The location of the file can either be based on the @code{prefix} variable, or be a standard location such as the user's home directory. It could even be specified by an environment variable. The programs should examine that file at run time, rather than at compile time. Run time configuration is more convenient for users and makes the configuration process simpler than getting the information while configuring. @xref{Directory Variables,, Variables for Installation Directories, standards, GNU Coding Standards}, for more information on where to put data files. @node Transforming Names, Site Defaults, Site Details, Site Configuration @section Transforming Program Names When Installing Autoconf supports changing the names of programs when installing them. In order to use these transformations, @file{configure.in} must call the macro @code{AC_ARG_PROGRAM}. @defmac AC_ARG_PROGRAM @maindex ARG_PROGRAM @ovindex program_transform_name Place in output variable @code{program_transform_name} a sequence of @code{sed} commands for changing the names of installed programs. If any of the options described below are given to @code{configure}, program names are transformed accordingly. Otherwise, if @code{AC_CANONICAL_TARGET} has been called and a @option{--target} value is given that differs from the host type (specified with @option{--host}), the target type followed by a dash is used as a prefix. Otherwise, no program name transformation is done. @end defmac @menu * Transformation Options:: @code{configure} options to transform names * Transformation Examples:: Sample uses of transforming names * Transformation Rules:: @file{Makefile} uses of transforming names @end menu @node Transformation Options, Transformation Examples, Transforming Names, Transforming Names @subsection Transformation Options You can specify name transformations by giving @code{configure} these command line options: @table @option @item --program-prefix=@var{prefix} prepend @var{prefix} to the names; @item --program-suffix=@var{suffix} append @var{suffix} to the names; @item --program-transform-name=@var{expression} perform @code{sed} substitution @var{expression} on the names. @end table @node Transformation Examples, Transformation Rules, Transformation Options, Transforming Names @subsection Transformation Examples These transformations are useful with programs that can be part of a cross-compilation development environment. For example, a cross-assembler running on a Sun 4 configured with @option{--target=i960-vxworks} is normally installed as @file{i960-vxworks-as}, rather than @file{as}, which could be confused with a native Sun 4 assembler. You can force a program name to begin with @file{g}, if you don't want @sc{gnu} programs installed on your system to shadow other programs with the same name. For example, if you configure @sc{gnu} @code{diff} with @option{--program-prefix=g}, then when you run @samp{make install} it is installed as @file{/usr/local/bin/gdiff}. As a more sophisticated example, you could use @example --program-transform-name='s/^/g/; s/^gg/g/; s/^gless/less/' @end example @noindent to prepend @samp{g} to most of the program names in a source tree, excepting those like @code{gdb} that already have one and those like @code{less} and @code{lesskey} that aren't @sc{gnu} programs. (That is assuming that you have a source tree containing those programs that is set up to use this feature.) One way to install multiple versions of some programs simultaneously is to append a version number to the name of one or both. For example, if you want to keep Autoconf version 1 around for awhile, you can configure Autoconf version 2 using @option{--program-suffix=2} to install the programs as @file{/usr/local/bin/autoconf2}, @file{/usr/local/bin/autoheader2}, etc. Nevertheless, pay attention that only the binaries are renamed, therefore you'd have problems with the library files which might overlap. @node Transformation Rules, , Transformation Examples, Transforming Names @subsection Transformation Rules Here is how to use the variable @code{program_transform_name} in a @file{Makefile.in}: @example transform = @@program_transform_name@@ install: all $(INSTALL_PROGRAM) myprog $(bindir)/`echo myprog|sed '$(transform)'` uninstall: rm -f $(bindir)/`echo myprog|sed '$(transform)'` @end example @noindent If you have more than one program to install, you can do it in a loop: @example PROGRAMS = cp ls rm install: for p in $(PROGRAMS); do \ $(INSTALL_PROGRAM) $$p $(bindir)/`echo $$p|sed '$(transform)'`; \ done uninstall: for p in $(PROGRAMS); do \ rm -f $(bindir)/`echo $$p|sed '$(transform)'`; \ done @end example Whether to do the transformations on documentation files (Texinfo or @code{man}) is a tricky question; there seems to be no perfect answer, due to the several reasons for name transforming. Documentation is not usually particular to a specific architecture, and Texinfo files do not conflict with system documentation. But they might conflict with earlier versions of the same files, and @code{man} pages sometimes do conflict with system documentation. As a compromise, it is probably best to do name transformations on @code{man} pages but not on Texinfo manuals. @node Site Defaults, , Transforming Names, Site Configuration @section Setting Site Defaults Autoconf-generated @code{configure} scripts allow your site to provide default values for some configuration values. You do this by creating site- and system-wide initialization files. @evindex CONFIG_SITE If the environment variable @code{CONFIG_SITE} is set, @code{configure} uses its value as the name of a shell script to read. Otherwise, it reads the shell script @file{@var{prefix}/share/config.site} if it exists, then @file{@var{prefix}/etc/config.site} if it exists. Thus, settings in machine-specific files override those in machine-independent ones in case of conflict. Site files can be arbitrary shell scripts, but only certain kinds of code are really appropriate to be in them. Because @code{configure} reads any cache file after it has read any site files, a site file can define a default cache file to be shared between all Autoconf-generated @code{configure} scripts run on that system. If you set a default cache file in a site file, it is a good idea to also set the output variable @code{CC} in that site file, because the cache file is only valid for a particular compiler, but many systems have several available. You can examine or override the value set by a command line option to @code{configure} in a site file; options set shell variables that have the same names as the options, with any dashes turned into underscores. The exceptions are that @option{--without-} and @option{--disable-} options are like giving the corresponding @option{--with-} or @option{--enable-} option and the value @samp{no}. Thus, @option{--cache-file=localcache} sets the variable @code{cache_file} to the value @samp{localcache}; @option{--enable-warnings=no} or @option{--disable-warnings} sets the variable @code{enable_warnings} to the value @samp{no}; @option{--prefix=/usr} sets the variable @code{prefix} to the value @samp{/usr}; etc. Site files are also good places to set default values for other output variables, such as @code{CFLAGS}, if you need to give them non-default values: anything you would normally do, repetitively, on the command line. If you use non-default values for @var{prefix} or @var{exec_prefix} (wherever you locate the site file), you can set them in the site file if you specify it with the @code{CONFIG_SITE} environment variable. You can set some cache values in the site file itself. Doing this is useful if you are cross-compiling, so it is impossible to check features that require running a test program. You could ``prime the cache'' by setting those values correctly for that system in @file{@var{prefix}/etc/config.site}. To find out the names of the cache variables you need to set, look for shell variables with @samp{_cv_} in their names in the affected @code{configure} scripts, or in the Autoconf M4 source code for those macros. The cache file is careful to not override any variables set in the site files. Similarly, you should not override command-line options in the site files. Your code should check that variables such as @code{prefix} and @code{cache_file} have their default values (as set near the top of @code{configure}) before changing them. Here is a sample file @file{/usr/share/local/gnu/share/config.site}. The command @samp{configure --prefix=/usr/share/local/gnu} would read this file (if @code{CONFIG_SITE} is not set to a different file). @example # config.site for configure # # Change some defaults. test "$prefix" = NONE && prefix=/usr/share/local/gnu test "$exec_prefix" = NONE && exec_prefix=/usr/local/gnu test "$sharedstatedir" = '$prefix/com' && sharedstatedir=/var test "$localstatedir" = '$prefix/var' && localstatedir=/var # Give Autoconf 2.x generated configure scripts a shared default # cache file for feature test results, architecture-specific. if test "$cache_file" = /dev/null; then cache_file="$prefix/var/config.cache" # A cache file is only valid for one C compiler. CC=gcc fi @end example @c ============================================== Running configure Scripts. @node Running configure scripts, config.status Invocation, Site Configuration, Top @chapter Running @code{configure} Scripts @cindex @code{configure} Below are instructions on how to configure a package that uses a @code{configure} script, suitable for inclusion as an @file{INSTALL} file in the package. A plain-text version of @file{INSTALL} which you may use comes with Autoconf. @menu * Basic Installation:: Instructions for typical cases * Compilers and Options:: Selecting compilers and optimization * Multiple Architectures:: Compiling for multiple architectures at once * Installation Names:: Installing in different directories * Optional Features:: Selecting optional features * System Type:: Specifying the system type * Sharing Defaults:: Setting site-wide defaults for @code{configure} * Environment Variables:: Defining environment variables. * configure Invocation:: Changing how @code{configure} runs @end menu @include install.texi @c ============================================== Recreating a Configuration @node config.status Invocation, Obsolete Constructs, Running configure scripts, Top @chapter Recreating a Configuration @cindex @code{config.status} The @code{configure} script creates a file named @file{config.status}, which actually configures, @dfn{instantiates}, the template files. It also records the configuration options that were specified when the package was last configured in case reconfiguring is needed. Synopsis: @example ./config.status @var{option}... [@var{file}@dots{}] @end example It configures the @var{files}, if none are specified, all the templates are instantiated. The files must be specified without their dependencies, as in @example ./config.status foobar @end example @noindent not @example ./config.status foobar:foo.in:bar.in @end example The supported @var{option}s are: @table @option @item --help @itemx -h Print a summary of the command line options, the list of the template files and exit. @item --version @itemx -V Print the version number of Autoconf and exit. @item --debug @itemx -d Don't remove the temporary files. @item --file=@var{file}[:@var{template}] Require that @var{file} be instantiated as if @samp{AC_CONFIG_FILES(@var{file}:@var{template})} was used. Both @var{file} and @var{template} may be @samp{-} in which case the standard output and/or standard input, respectively, is used. If a @var{template} filename is relative, it is first looked for in the build tree, and then in the source tree. @xref{Configuration Actions}, for more details. This option and the following ones provide one way for separately distributed packages to share the values computed by @code{configure}. Doing so can be useful if some of the packages need a superset of the features that one of them, perhaps a common library, does. These options allow a @file{config.status} file to create files other than the ones that its @file{configure.in} specifies, so it can be used for a different package. @item --header=@var{file}[:@var{template}] Same as @option{--file} above, but with @samp{AC_CONFIG_HEADERS}. @item --recheck Ask @file{config.status} to update itself and exit (no instantiation). This option is useful if you change @code{configure}, so that the results of some tests might be different from the previous run. The @option{--recheck} option re-runs @code{configure} with the same arguments you used before, plus the @option{--no-create} option, which prevents @code{configure} from running @file{config.status} and creating @file{Makefile} and other files, and the @option{--no-recursion} option, which prevents @code{configure} from running other @code{configure} scripts in subdirectories. (This is so other @file{Makefile} rules can run @file{config.status} when it changes; @pxref{Automatic Remaking}, for an example). @end table @file{config.status} checks several optional environment variables that can alter its behavior: @defvar CONFIG_SHELL @evindex CONFIG_SHELL The shell with which to run @code{configure} for the @option{--recheck} option. It must be Bourne-compatible. The default is @file{/bin/sh}. @end defvar @defvar CONFIG_STATUS @evindex CONFIG_STATUS The file name to use for the shell script that records the configuration. The default is @file{./config.status}. This variable is useful when one package uses parts of another and the @code{configure} scripts shouldn't be merged because they are maintained separately. @end defvar You can use @file{./config.status} in your Makefiles. For example, in the dependencies given above (@pxref{Automatic Remaking}), @file{config.status} is run twice when @file{configure.in} has changed. If that bothers you, you can make each run only regenerate the files for that rule: @example @group config.h: stamp-h stamp-h: config.h.in config.status ./config.status config.h echo > stamp-h Makefile: Makefile.in config.status ./config.status Makefile @end group @end example The calling convention of @file{config.status} has changed, see @ref{Obsolete config.status Use}, for details. @c =================================================== Obsolete Constructs @node Obsolete Constructs, Questions, config.status Invocation, Top @chapter Obsolete Constructs Autoconf changes, and throughout the years some constructs are obsoleted. Most of the changes involve the macros, but the tools themselves, or even some concepts, are now considered obsolete. You may completely skip this chapter if you are new to Autoconf, its intention is mainly to help maintainers updating their packages by understanding how to move to more modern constructs. @menu * Obsolete config.status Use:: Different calling convention * acconfig.h:: Additional entries in @file{config.h.in} * autoupdate Invocation:: Automatic update of @file{configure.in} * Obsolete Macros:: Backward compatibility macros * Autoconf 1:: Tips for upgrading your files @end menu @node Obsolete config.status Use, acconfig.h, Obsolete Constructs, Obsolete Constructs @section Obsolete @file{config.status} Invocation @file{config.status} now supports arguments to specify the files to instantiate, see @ref{config.status Invocation}, for more details. Before, environment variables had to be used. @defvar CONFIG_COMMANDS @evindex CONFIG_COMMANDS The tags of the commands to execute. The default is the arguments given to @code{AC_OUTPUT} and @code{AC_CONFIG_COMMANDS} in @file{configure.in}. @end defvar @defvar CONFIG_FILES @evindex CONFIG_FILES The files in which to perform @samp{@@@var{variable}@@} substitutions. The default is the arguments given to @code{AC_OUTPUT} and @code{AC_CONFIG_FILES} in @file{configure.in}. @end defvar @defvar CONFIG_HEADERS @evindex CONFIG_HEADERS The files in which to substitute C @code{#define} statements. The default is the arguments given to @code{AC_CONFIG_HEADERS}; if that macro was not called, @file{config.status} ignores this variable. @end defvar @defvar CONFIG_LINKS @evindex CONFIG_LINKS The symbolic links to establish. The default is the arguments given to @code{AC_CONFIG_LINKS}; if that macro was not called, @file{config.status} ignores this variable. @end defvar In @ref{config.status Invocation}, using this old interface, the example would be: @example @group config.h: stamp-h stamp-h: config.h.in config.status CONFIG_COMMANDS= CONFIG_LINKS= CONFIG_FILES= \ CONFIG_HEADERS=config.h ./config.status echo > stamp-h Makefile: Makefile.in config.status CONFIG_COMMANDS= CONFIG_LINKS= CONFIG_HEADERS= \ CONFIG_FILES=Makefile ./config.status @end group @end example @noindent (If @file{configure.in} does not call @code{AC_CONFIG_HEADERS}, there is no need to set @code{CONFIG_HEADERS} in the @code{make} rules, equally for @code{CONFIG_COMMANDS} etc.) @node acconfig.h, autoupdate Invocation, Obsolete config.status Use, Obsolete Constructs @section @file{acconfig.h} @cindex @file{acconfig.h} @cindex @file{config.h.top} @cindex @file{config.h.bot} @code{autoheader} scans @file{configure.in} and figures out which C preprocessor symbols it might define. It copies comments and @code{#define} and @code{#undef} statements from a file called @file{acconfig.h} in the current directory, if present. This file used to be mandatory if you @code{AC_DEFINE} any additional symbols. Now, you are encouraged to use the @code{AH} series of macros (@pxref{Autoheader Macros}). The file that @code{autoheader} creates contains mainly @code{#define} and @code{#undef} statements and their accompanying comments. If @file{./acconfig.h} contains the string @samp{@@TOP@@}, @code{autoheader} copies the lines before the line containing @samp{@@TOP@@} into the top of the file that it generates. Similarly, if @file{./acconfig.h} contains the string @samp{@@BOTTOM@@}, @code{autoheader} copies the lines after that line to the end of the file it generates. Either or both of those strings may be omitted. An alternate way to produce the same effect is to create the files @file{@var{file}.top} (typically @file{config.h.top}) and/or @file{@var{file}.bot} in the current directory. If they exist, @code{autoheader} copies them to the beginning and end, respectively, of its output. Their use is discouraged because they have file names that contain two periods, and so cannot be stored on MS-DOS; also, they are two more files to clutter up the directory. But if you use the @option{--localdir=@var{dir}} option to use an @file{acconfig.h} in another directory, they give you a way to put custom boilerplate in each individual @file{config.h.in}. @node autoupdate Invocation, Obsolete Macros, acconfig.h, Obsolete Constructs @section Using @code{autoupdate} to Modernize @file{configure.in} @cindex @code{autoupdate} The @code{autoupdate} program updates a @file{configure.in} file that calls Autoconf macros by their old names to use the current macro names. In version 2 of Autoconf, most of the macros were renamed to use a more uniform and descriptive naming scheme. @xref{Macro Names}, for a description of the new scheme. Although the old names still work (@pxref{Obsolete Macros}, for a list of the old macros and the corresponding new names), you can make your @file{configure.in} files more readable and make it easier to use the current Autoconf documentation if you update them to use the new macro names. @evindex SIMPLE_BACKUP_SUFFIX If given no arguments, @code{autoupdate} updates @file{configure.in}, backing up the original version with the suffix @file{~} (or the value of the environment variable @code{SIMPLE_BACKUP_SUFFIX}, if that is set). If you give @code{autoupdate} an argument, it reads that file instead of @file{configure.in} and writes the updated file to the standard output. @noindent @code{autoupdate} accepts the following options: @table @option @item --help @itemx -h Print a summary of the command line options and exit. @item --version @itemx -V Print the version number of Autoconf and exit. @item --verbose @itemx -v Report processing steps. @item --debug @itemx -d Don't remove the temporary files. @item --autoconf-dir=@var{dir} @itemx -A @evindex AC_MACRODIR Overwrite the location where Autoconf files were installed. You can also set the @code{AC_MACRODIR} environment variable to a directory; this option overrides the environment variable. This option is rarely needed and dangerous: only when you play with different versions of Autoconf. @item --localdir=@var{dir} @itemx -l @var{dir} Look for the package file @file{aclocal.m4} in directory @var{dir} instead of in the current directory. @end table @node Obsolete Macros, Autoconf 1, autoupdate Invocation, Obsolete Constructs @section Obsolete Macros Several macros are obsoleted in Autoconf, for various reasons (typically they failed to quote properly, couldn't be extended for more recent issues etc.). They are still supported, but deprecated: their use should be avoided. During the jump from Autoconf version 1 to version 2, most of the macros were renamed to use a more uniform and descriptive naming scheme, but their signature did not change. @xref{Macro Names}, for a description of the new naming scheme. Below, there is just the mapping from old names to new names for these macros, the reader is invited to refer to the definition of the new macro for the signature and the description. @defmac AC_ALLOCA @maindex ALLOCA @code{AC_FUNC_ALLOCA} @end defmac @defmac AC_ARG_ARRAY @maindex ARG_ARRAY removed because of limited usefulness @end defmac @defmac AC_C_CROSS @maindex C_CROSS This macro is obsolete; it does nothing. @end defmac @defmac AC_CANONICAL_SYSTEM @maindex CANONICAL_SYSTEM Determine the system type and set output variables to the names of the canonical system types. @xref{Canonicalizing}, for details about the variables this macro sets. The user is encouraged to explicitly use either @code{AC_CANONICAL_BUILD}, or @code{AC_CANONICAL_HOST}, or @code{AC_CANONICAL_TARGET}, depending on her needs. Using @code{AC_CANONICAL_TARGET} is enough to run the three macros. @end defmac @defmac AC_CHAR_UNSIGNED @maindex CHAR_UNSIGNED @code{AC_C_CHAR_UNSIGNED} @end defmac @defmac AC_CHECK_TYPE (@var{type}, @var{default}) @maindex CHECK_TYPE Autoconf, up to 2.13, used to provide this version of @code{AC_CHECK_TYPE}, deprecated because of its flaws. Firstly, although it is a member of the @code{CHECK} clan, singular sub-family, it does more than just checking. Second, missing types are not @code{typedef}'d, they are @code{#define}'d, which can lead to incompatible code in the case of pointer types. This use of @code{AC_CHECK_TYPE} is obsolete and discouraged, see @ref{Generic Types}, for the description of the current macro. If the type @var{type} is not defined, define it to be the C (or C++) builtin type @var{default}; e.g., @samp{short} or @samp{unsigned}. This macro is equivalent to: @example AC_CHECK_TYPE([@var{type}], [AC_DEFINE([@var{type}], [@var{default}], [Define to `@var{default}' if does not define.])]) @end example In order to keep backward compatibility, the two versions of @code{AC_CHECK_TYPE} are implemented, selected by a simple heuristics: @enumerate @item If there are three or four arguments, the modern version is used. @item If the second argument is a C or C++ @emph{builtin} type, then the obsolete version is used. Because many people have used @samp{off_t} and @samp{size_t} as replacement types, they are recognized too. @item If the second argument is spelled with the alphabet of valid C and C++ types, the user is warned and the modern version is used. @item Otherwise, the modern version is used. @end enumerate @noindent You are encouraged either to use a valid builtin type, or to use the equivalent modern code (see above), or better yet, to use @code{AC_CHECK_TYPES} together with @example #if !HAVE_LOFF_T typedef loff_t off_t; #endif @end example @end defmac @c end of AC_CHECK_TYPE @defmac AC_CHECKING (@var{feature-description}) @maindex CHECKING Same as @samp{AC_MSG_NOTICE([checking @var{feature-description}...]}. @end defmac @defmac AC_COMPILE_CHECK (@var{echo-text}, @var{includes}, @var{function-body}, @var{action-if-found}, @ovar{action-if-not-found}) @maindex COMPILE_CHECK This is an obsolete version of @code{AC_TRY_LINK} (@pxref{Examining Libraries}), with the addition that it prints @samp{checking for @var{echo-text}} to the standard output first, if @var{echo-text} is non-empty. Use @code{AC_MSG_CHECKING} and @code{AC_MSG_RESULT} instead to print messages (@pxref{Printing Messages}). @end defmac @defmac AC_CONST @maindex CONST @code{AC_C_CONST} @end defmac @defmac AC_CROSS_CHECK @maindex CROSS_CHECK Same as @code{AC_C_CROSS}, which is obsolete too, and does nothing @code{:-)}. @end defmac @defmac AC_CYGWIN @maindex CYGWIN Checked for the Cygwin environment in which case the shell variable @code{CYGWIN} is set to @samp{yes}. @code{AC_EXEEXT} now handles this task. @end defmac @defmac AC_DECL_YYTEXT @maindex DECL_YYTEXT Does nothing, now integrated in @code{AC_PROG_LEX}. @end defmac @defmac AC_DIR_HEADER @maindex DIR_HEADER @cvindex DIRENT @cvindex SYSNDIR @cvindex SYSDIR @cvindex NDIR Like calling @code{AC_FUNC_CLOSEDIR_VOID} and@code{AC_HEADER_DIRENT}, but defines a different set of C preprocessor macros to indicate which header file is found: @multitable {@file{sys/ndir.h}} {Old Symbol} {@code{HAVE_SYS_NDIR_H}} @item Header @tab Old Symbol @tab New Symbol @item @file{dirent.h} @tab @code{DIRENT} @tab @code{HAVE_DIRENT_H} @item @file{sys/ndir.h} @tab @code{SYSNDIR} @tab @code{HAVE_SYS_NDIR_H} @item @file{sys/dir.h} @tab @code{SYSDIR} @tab @code{HAVE_SYS_DIR_H} @item @file{ndir.h} @tab @code{NDIR} @tab @code{HAVE_NDIR_H} @end multitable @end defmac @defmac AC_DYNIX_SEQ @maindex DYNIX_SEQ If on Dynix/PTX (Sequent @sc{unix}), add @option{-lseq} to output variable @code{LIBS}. This macro used to be defined as @example AC_CHECK_LIB(seq, getmntent, LIBS="-lseq $LIBS") @end example @noindent now it is just @code{AC_FUNC_GETMNTENT}. @end defmac @defmac AC_EXEEXT @maindex EXEEXT @ovindex EXEEXT @ovindex CYGWIN @ovindex EMXOS2 @ovindex MINGW32 Defined the output variable @code{EXEEXT} based on the output of the compiler. Typically set to empty string if Unix and @samp{.exe} if Win32 or OS/2. This macro sets the shell variable @code{CYGWIN} to @samp{yes} if run in the Cygwin environment, @code{EMXOS2} to @samp{yes} if in the EMX environment on OS/2, and @code{MINGW32} to @samp{yes} with the MingW32 compiler. Now handled by the macros checking for the compiler. @end defmac @defmac AC_EMXOS2 @maindex EMXOS2 Checks for the EMX environment on OS/2 in which case the shell variable @code{EMXOS2} is set to @samp{yes}. @code{AC_EXEEXT} now handles this task. @end defmac @defmac AC_ERROR @maindex ERROR @code{AC_MSG_ERROR} @end defmac @defmac AC_FIND_X @maindex FIND_X @code{AC_PATH_X} @end defmac @defmac AC_FIND_XTRA @maindex FIND_XTRA @code{AC_PATH_XTRA} @end defmac @defmac AC_FUNC_CHECK @maindex FUNC_CHECK @code{AC_CHECK_FUNC} @end defmac @defmac AC_GCC_TRADITIONAL @maindex GCC_TRADITIONAL @code{AC_PROG_GCC_TRADITIONAL} @end defmac @defmac AC_GETGROUPS_T @maindex GETGROUPS_T @code{AC_TYPE_GETGROUPS} @end defmac @defmac AC_GETLOADAVG @maindex GETLOADAVG @code{AC_FUNC_GETLOADAVG} @end defmac @defmac AC_HAVE_FUNCS @maindex HAVE_FUNCS @code{AC_CHECK_FUNCS} @end defmac @defmac AC_HAVE_HEADERS @maindex HAVE_HEADERS @code{AC_CHECK_HEADERS} @end defmac @defmac AC_HAVE_LIBRARY (@var{library}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{other-libraries}) @maindex HAVE_LIBRARY This macro is equivalent to calling @code{AC_CHECK_LIB} with a @var{function} argument of @code{main}. In addition, @var{library} can be written as any of @samp{foo}, @option{-lfoo}, or @samp{libfoo.a}. In all of those cases, the compiler is passed @option{-lfoo}. However, @var{library} cannot be a shell variable; it must be a literal name. @end defmac @defmac AC_HAVE_POUNDBANG @maindex HAVE_POUNDBANG @code{AC_SYS_INTERPRETER} (different calling convention) @end defmac @defmac AC_HEADER_CHECK @maindex HEADER_CHECK @code{AC_CHECK_HEADER} @end defmac @defmac AC_HEADER_EGREP @maindex HEADER_EGREP @code{AC_EGREP_HEADER} @end defmac @defmac AC_INIT (@var{unique-file-in-source-dir}) @maindex INIT Formerly @code{AC_INIT} used to have a single argument, and was equivalent to: @example AC_INIT AC_CONFIG_SRCDIR(@var{unique-file-in-source-dir}) @end example @end defmac @defmac AC_INLINE @maindex INLINE @code{AC_C_INLINE} @end defmac @defmac AC_INT_16_BITS @maindex INT_16_BITS @cvindex INT_16_BITS If the C type @code{int} is 16 bits wide, define @code{INT_16_BITS}. Use @samp{AC_CHECK_SIZEOF(int)} instead. @end defmac @defmac AC_IRIX_SUN @maindex IRIX_SUN If on IRIX (Silicon Graphics @sc{unix}), add @option{-lsun} to output @code{LIBS}. If you were using it to get @code{getmntent}, use @code{AC_FUNC_GETMNTENT} instead. If you used it for the NIS versions of the password and group functions, use @samp{AC_CHECK_LIB(sun, getpwnam)}. Up to Autoconf 2.13, it used to be @example AC_CHECK_LIB(sun, getmntent, LIBS="-lsun $LIBS") @end example @noindent now it is defined as @example AC_FUNC_GETMNTENT AC_CHECK_LIB(sun, getpwnam) @end example @end defmac @defmac AC_LANG_C @maindex LANG_C Same as @samp{AC_LANG(C)}. @end defmac @defmac AC_LANG_CPLUSPLUS @maindex LANG_CPLUSPLUS Same as @samp{AC_LANG(C++)}. @end defmac @defmac AC_LANG_FORTRAN77 @maindex LANG_FORTRAN77 Same as @samp{AC_LANG(Fortran 77)}. @end defmac @defmac AC_LANG_RESTORE @maindex LANG_RESTORE Select the @var{language} that is saved on the top of the stack, as set by @code{AC_LANG_SAVE}, remove it from the stack, and call @code{AC_LANG(@var{language})}. @end defmac @defmac AC_LANG_SAVE @maindex LANG_SAVE Remember the current language (as set by @code{AC_LANG}) on a stack. Doe not change which language is current. @code{AC_LANG_PUSH} is preferred. @end defmac @defmac AC_LINK_FILES (@var{source}@dots{}, @var{dest}@dots{}) @maindex LINK_FILES This is an obsolete version of @code{AC_CONFIG_LINKS}. An updated version of: @example AC_LINK_FILES(config/$machine.h config/$obj_format.h, host.h object.h) @end example @noindent is: @example AC_CONFIG_LINKS(host.h:config/$machine.h object.h:config/$obj_format.h) @end example @end defmac @defmac AC_LN_S @maindex LN_S @code{AC_PROG_LN_S} @end defmac @defmac AC_LONG_64_BITS @maindex LONG_64_BITS @cvindex LONG_64_BITS If the C type @code{long int} is 16 bits wide, define @code{LONG_64_BITS}. Use @samp{AC_CHECK_SIZEOF(long int)} instead. @end defmac @defmac AC_LONG_DOUBLE @maindex LONG_DOUBLE @code{AC_C_LONG_DOUBLE} @end defmac @defmac AC_LONG_FILE_NAMES @maindex LONG_FILE_NAMES @code{AC_SYS_LONG_FILE_NAMES} @end defmac @defmac AC_MAJOR_HEADER @maindex MAJOR_HEADER @code{AC_HEADER_MAJOR} @end defmac @defmac AC_MEMORY_H @maindex MEMORY_H @cvindex NEED_MEMORY_H Used to define @code{NEED_MEMORY_H} if the @code{mem} functions were defined in @file{memory.h}. Today it is equivalent to @samp{AC_CHECK_HEADERS(memory.h)}. Adjust your code to depend upon @code{HAVE_MEMORY_H}, not @code{NEED_MEMORY_H}, see @xref{Standard Symbols}. @end defmac @defmac AC_MINGW32 @maindex MINGW32 Checked for the MingW32 compiler environment, in which case the shell variable @code{MINGW32} is set to @samp{yes}. @code{AC_EXEEXT} now handles this task. @end defmac @defmac AC_MINUS_C_MINUS_O @maindex MINUS_C_MINUS_O @code{AC_PROG_CC_C_O} @end defmac @defmac AC_MMAP @maindex MMAP @code{AC_FUNC_MMAP} @end defmac @defmac AC_MODE_T @maindex MODE_T @code{AC_TYPE_MODE_T} @end defmac @defmac AC_OBJEXT @maindex OBJEXT @ovindex OBJEXT Defined the output variable @code{OBJEXT} based on the output of the compiler, after .c files have been excluded. Typically set to @samp{o} if Unix, @samp{obj} if Win32. Now the compiler checking macros handle this. @end defmac @defmac AC_OBSOLETE (@var{this-macro-name}, @ovar{suggestion}) @maindex OBSOLETE Make @code{m4} print a message on the standard error output warning that @var{this-macro-name} is obsolete, and giving the file and line number where it was called. @var{this-macro-name} should be the name of the macro that is calling @code{AC_OBSOLETE}. If @var{suggestion} is given, it is printed at the end of the warning message; for example, it can be a suggestion for what to use instead of @var{this-macro-name}. For instance @example AC_OBSOLETE([$0], [; use AC_CHECK_HEADERS(unistd.h) instead])dnl @end example You are encouraged to use @code{AU_DEFUN} instead, since it gives better services to the user. @end defmac @defmac AC_OFF_T @maindex OFF_T @code{AC_TYPE_OFF_T} @end defmac @defmac AC_OUTPUT (@ovar{file}@dots{}, @ovar{extra-cmds}, @ovar{init-cmds}) @maindex OUTPUT The use of @code{AC_OUTPUT} with argument is deprecated, this obsoleted interface is equivalent to: @example @group AC_CONFIG_FILES(@var{file}@dots{}) AC_CONFIG_COMMANDS([default], @var{extra-cmds}, @var{init-cmds}) AC_OUTPUT @end group @end example @end defmac @defmac AC_OUTPUT_COMMANDS (@var{extra-cmds}, @ovar{init-cmds}) @maindex OUTPUT_COMMANDS Specify additional shell commands to run at the end of @file{config.status}, and shell commands to initialize any variables from @code{configure}. This macro may be called multiple times. It is obsolete, replaced by @code{AC_CONFIG_COMMANDS}. Here is an unrealistic example: @example fubar=27 AC_OUTPUT_COMMANDS([echo this is extra $fubar, and so on.], fubar=$fubar) AC_OUTPUT_COMMANDS([echo this is another, extra, bit], [echo init bit]) @end example Aside from the fact that @code{AC_CONFIG_COMMANDS} requires an additional key, an important difference is that @code{AC_OUTPUT_COMMANDS} is quoting its arguments twice, while @code{AC_CONFIG_COMMANDS}. This means that @code{AC_CONFIG_COMMANDS} can safely be given macro calls as arguments: @example AC_CONFIG_COMMANDS(foo, [my_FOO()]) @end example @noindent conversely, where one level of quoting was enough for literal strings with @code{AC_OUTPUT_COMMANDS}, you need two with @code{AC_CONFIG_COMMANDS}. The following lines are equivalent: @example @group AC_OUTPUT_COMMANDS([echo "Square brackets: []"]) AC_CONFIG_COMMANDS(default, [[echo "Square brackets: []"]]) @end group @end example @end defmac @defmac AC_PID_T @maindex PID_T @code{AC_TYPE_PID_T} @end defmac @defmac AC_PREFIX @maindex PREFIX @code{AC_PREFIX_PROGRAM} @end defmac @defmac AC_PROGRAMS_CHECK @maindex PROGRAMS_CHECK @code{AC_CHECK_PROGS} @end defmac @defmac AC_PROGRAMS_PATH @maindex PROGRAMS_PATH @code{AC_PATH_PROGS} @end defmac @defmac AC_PROGRAM_CHECK @maindex PROGRAM_CHECK @code{AC_CHECK_PROG} @end defmac @defmac AC_PROGRAM_EGREP @maindex PROGRAM_EGREP @code{AC_EGREP_CPP} @end defmac @defmac AC_PROGRAM_PATH @maindex PROGRAM_PATH @code{AC_PATH_PROG} @end defmac @defmac AC_REMOTE_TAPE @maindex REMOTE_TAPE removed because of limited usefulness @end defmac @defmac AC_RESTARTABLE_SYSCALLS @maindex RESTARTABLE_SYSCALLS @code{AC_SYS_RESTARTABLE_SYSCALLS} @end defmac @defmac AC_RETSIGTYPE @maindex RETSIGTYPE @code{AC_TYPE_SIGNAL} @end defmac @defmac AC_RSH @maindex RSH Removed because of limited usefulness. @end defmac @defmac AC_SCO_INTL @maindex SCO_INTL @ovindex LIBS If on SCO UNIX, add @option{-lintl} to output variable @code{LIBS}. This macro used to @example AC_CHECK_LIB(intl, strftime, LIBS="-lintl $LIBS") @end example @noindent now it just calls @code{AC_FUNC_STRFTIME} instead. @end defmac @defmac AC_SETVBUF_REVERSED @maindex SETVBUF_REVERSED @code{AC_FUNC_SETVBUF_REVERSED} @end defmac @defmac AC_SET_MAKE @maindex SET_MAKE @code{AC_PROG_MAKE_SET} @end defmac @defmac AC_SIZEOF_TYPE @maindex SIZEOF_TYPE @code{AC_CHECK_SIZEOF} @end defmac @defmac AC_SIZE_T @maindex SIZE_T @code{AC_TYPE_SIZE_T} @end defmac @defmac AC_STAT_MACROS_BROKEN @maindex STAT_MACROS_BROKEN @code{AC_HEADER_STAT} @end defmac @defmac AC_STDC_HEADERS @maindex STDC_HEADERS @code{AC_HEADER_STDC} @end defmac @defmac AC_STRCOLL @maindex STRCOLL @code{AC_FUNC_STRCOLL} @end defmac @defmac AC_ST_BLKSIZE @maindex ST_BLKSIZE @code{AC_STRUCT_ST_BLKSIZE} @end defmac @defmac AC_ST_BLOCKS @maindex ST_BLOCKS @code{AC_STRUCT_ST_BLOCKS} @end defmac @defmac AC_ST_RDEV @maindex ST_RDEV @code{AC_STRUCT_ST_RDEV} @end defmac @defmac AC_SYS_SIGLIST_DECLARED @maindex SYS_SIGLIST_DECLARED @code{AC_DECL_SYS_SIGLIST} @end defmac @defmac AC_TEST_CPP @maindex TEST_CPP @code{AC_TRY_CPP} @end defmac @defmac AC_TEST_PROGRAM @maindex TEST_PROGRAM @code{AC_TRY_RUN} @end defmac @defmac AC_TIMEZONE @maindex TIMEZONE @code{AC_STRUCT_TIMEZONE} @end defmac @defmac AC_TIME_WITH_SYS_TIME @maindex TIME_WITH_SYS_TIME @code{AC_HEADER_TIME} @end defmac @defmac AC_UID_T @maindex UID_T @code{AC_TYPE_UID_T} @end defmac @defmac AC_UNISTD_H @maindex UNISTD_H Same as @samp{AC_CHECK_HEADERS(unistd.h)}. @end defmac @defmac AC_USG @maindex USG @cvindex USG Define @code{USG} if the @sc{bsd} string functions are defined in @file{strings.h}. You should no longer depend upon @code{USG}, but on @code{HAVE_STRING_H}, see @xref{Standard Symbols}. @end defmac @defmac AC_UTIME_NULL @maindex UTIME_NULL @code{AC_FUNC_UTIME_NULL} @end defmac @defmac AC_VALIDATE_CACHED_SYSTEM_TUPLE (@ovar{cmd}) @maindex VALIDATE_CACHED_SYSTEM_TUPLE If the cache file is inconsistent with the current host, target and build system types, it used to execute @var{cmd} or print a default error message. This is now handled by default. @end defmac @defmac AC_VERBOSE (@var{result-description}) @maindex VERBOSE @code{AC_MSG_RESULT}. @end defmac @defmac AC_VFORK @maindex VFORK @code{AC_FUNC_VFORK} @end defmac @defmac AC_VPRINTF @maindex VPRINTF @code{AC_FUNC_VPRINTF} @end defmac @defmac AC_WAIT3 @maindex WAIT3 @code{AC_FUNC_WAIT3} @end defmac @defmac AC_WARN @maindex WARN @code{AC_MSG_WARN} @end defmac @defmac AC_WORDS_BIGENDIAN @maindex WORDS_BIGENDIAN @code{AC_C_BIGENDIAN} @end defmac @defmac AC_XENIX_DIR @maindex XENIX_DIR @ovindex LIBS This macro used to add @option{-lx} to output variable @code{LIBS} if on Xenix. Also, if @file{dirent.h} is being checked for, added @option{-ldir} to @code{LIBS}. Now it is merely an alias of @code{AC_HEADER_DIRENT} instead, plus some code to detect whether running @sc{xenix} on which you should not depend: @example AC_MSG_CHECKING(for Xenix) AC_EGREP_CPP(yes, [#if defined M_XENIX && !defined M_UNIX yes #endif], [AC_MSG_RESULT(yes); XENIX=yes], [AC_MSG_RESULT(no); XENIX=]) @end example @end defmac @defmac AC_YYTEXT_POINTER @maindex YYTEXT_POINTER @code{AC_DECL_YYTEXT} @end defmac @node Autoconf 1, , Obsolete Macros, Obsolete Constructs @section Upgrading From Version 1 Autoconf version 2 is mostly backward compatible with version 1. However, it introduces better ways to do some things, and doesn't support some of the ugly things in version 1. So, depending on how sophisticated your @file{configure.in} files are, you might have to do some manual work in order to upgrade to version 2. This chapter points out some problems to watch for when upgrading. Also, perhaps your @code{configure} scripts could benefit from some of the new features in version 2; the changes are summarized in the file @file{NEWS} in the Autoconf distribution. @menu * Changed File Names:: Files you might rename * Changed Makefiles:: New things to put in @file{Makefile.in} * Changed Macros:: Macro calls you might replace * Changed Results:: Changes in how to check test results * Changed Macro Writing:: Better ways to write your own macros @end menu @node Changed File Names, Changed Makefiles, Autoconf 1, Autoconf 1 @subsection Changed File Names If you have an @file{aclocal.m4} installed with Autoconf (as opposed to in a particular package's source directory), you must rename it to @file{acsite.m4}. @xref{autoconf Invocation}. If you distribute @file{install.sh} with your package, rename it to @file{install-sh} so @code{make} builtin rules won't inadvertently create a file called @file{install} from it. @code{AC_PROG_INSTALL} looks for the script under both names, but it is best to use the new name. If you were using @file{config.h.top} or @file{config.h.bot}, you still can, but you will have less clutter if you merge them into @file{acconfig.h}. @xref{autoheader Invocation}. @node Changed Makefiles, Changed Macros, Changed File Names, Autoconf 1 @subsection Changed Makefiles Add @samp{@@CFLAGS@@}, @samp{@@CPPFLAGS@@}, and @samp{@@LDFLAGS@@} in your @file{Makefile.in} files, so they can take advantage of the values of those variables in the environment when @code{configure} is run. Doing this isn't necessary, but it's a convenience for users. Also add @samp{@@configure_input@@} in a comment to each input file for @code{AC_OUTPUT}, so that the output files will contain a comment saying they were produced by @code{configure}. Automatically selecting the right comment syntax for all the kinds of files that people call @code{AC_OUTPUT} on became too much work. Add @file{config.log} and @file{config.cache} to the list of files you remove in @code{distclean} targets. If you have the following in @file{Makefile.in}: @example prefix = /usr/local exec_prefix = $(prefix) @end example @noindent you must change it to: @example prefix = @@prefix@@ exec_prefix = @@exec_prefix@@ @end example @noindent The old behavior of replacing those variables without @samp{@@} characters around them has been removed. @node Changed Macros, Changed Results, Changed Makefiles, Autoconf 1 @subsection Changed Macros Many of the macros were renamed in Autoconf version 2. You can still use the old names, but the new ones are clearer, and it's easier to find the documentation for them. @xref{Obsolete Macros}, for a table showing the new names for the old macros. Use the @code{autoupdate} program to convert your @file{configure.in} to using the new macro names. @xref{autoupdate Invocation}. Some macros have been superseded by similar ones that do the job better, but are not call-compatible. If you get warnings about calling obsolete macros while running @code{autoconf}, you may safely ignore them, but your @code{configure} script will generally work better if you follow the advice it prints about what to replace the obsolete macros with. In particular, the mechanism for reporting the results of tests has changed. If you were using @code{echo} or @code{AC_VERBOSE} (perhaps via @code{AC_COMPILE_CHECK}), your @code{configure} script's output will look better if you switch to @code{AC_MSG_CHECKING} and @code{AC_MSG_RESULT}. @xref{Printing Messages}. Those macros work best in conjunction with cache variables. @xref{Caching Results}. @node Changed Results, Changed Macro Writing, Changed Macros, Autoconf 1 @subsection Changed Results If you were checking the results of previous tests by examining the shell variable @code{DEFS}, you need to switch to checking the values of the cache variables for those tests. @code{DEFS} no longer exists while @code{configure} is running; it is only created when generating output files. This difference from version 1 is because properly quoting the contents of that variable turned out to be too cumbersome and inefficient to do every time @code{AC_DEFINE} is called. @xref{Cache Variable Names}. For example, here is a @file{configure.in} fragment written for Autoconf version 1: @example AC_HAVE_FUNCS(syslog) case "$DEFS" in *-DHAVE_SYSLOG*) ;; *) # syslog is not in the default libraries. See if it's in some other. saved_LIBS="$LIBS" for lib in bsd socket inet; do AC_CHECKING(for syslog in -l$lib) LIBS="$saved_LIBS -l$lib" AC_HAVE_FUNCS(syslog) case "$DEFS" in *-DHAVE_SYSLOG*) break ;; *) ;; esac LIBS="$saved_LIBS" done ;; esac @end example Here is a way to write it for version 2: @example AC_CHECK_FUNCS(syslog) if test $ac_cv_func_syslog = no; then # syslog is not in the default libraries. See if it's in some other. for lib in bsd socket inet; do AC_CHECK_LIB($lib, syslog, [AC_DEFINE(HAVE_SYSLOG) LIBS="$LIBS -l$lib"; break]) done fi @end example If you were working around bugs in @code{AC_DEFINE_UNQUOTED} by adding backslashes before quotes, you need to remove them. It now works predictably, and does not treat quotes (except back quotes) specially. @xref{Setting Output Variables}. All of the boolean shell variables set by Autoconf macros now use @samp{yes} for the true value. Most of them use @samp{no} for false, though for backward compatibility some use the empty string instead. If you were relying on a shell variable being set to something like 1 or @samp{t} for true, you need to change your tests. @node Changed Macro Writing, , Changed Results, Autoconf 1 @subsection Changed Macro Writing When defining your own macros, you should now use @code{AC_DEFUN} instead of @code{define}. @code{AC_DEFUN} automatically calls @code{AC_PROVIDE} and ensures that macros called via @code{AC_REQUIRE} do not interrupt other macros, to prevent nested @samp{checking@dots{}} messages on the screen. There's no actual harm in continuing to use the older way, but it's less convenient and attractive. @xref{Macro Definitions}. You probably looked at the macros that came with Autoconf as a guide for how to do things. It would be a good idea to take a look at the new versions of them, as the style is somewhat improved and they take advantage of some new features. If you were doing tricky things with undocumented Autoconf internals (macros, variables, diversions), check whether you need to change anything to account for changes that have been made. Perhaps you can even use an officially supported technique in version 2 instead of kludging. Or perhaps not. To speed up your locally written feature tests, add caching to them. See whether any of your tests are of general enough usefulness to encapsulate into macros that you can share. @c ================================================ Questions About Autoconf. @node Questions, History, Obsolete Constructs, Top @chapter Questions About Autoconf Several questions about Autoconf come up occasionally. Here some of them are addressed. @menu * Distributing:: Distributing @code{configure} scripts * Why GNU m4:: Why not use the standard M4? * Bootstrapping:: Autoconf and GNU M4 require each other? * Why Not Imake:: Why GNU uses @code{configure} instead of Imake @end menu @node Distributing, Why GNU m4, Questions, Questions @section Distributing @code{configure} Scripts @display What are the restrictions on distributing @code{configure} scripts that Autoconf generates? How does that affect my programs that use them? @end display There are no restrictions on how the configuration scripts that Autoconf produces may be distributed or used. In Autoconf version 1, they were covered by the @sc{gnu} General Public License. We still encourage software authors to distribute their work under terms like those of the GPL, but doing so is not required to use Autoconf. Of the other files that might be used with @code{configure}, @file{config.h.in} is under whatever copyright you use for your @file{configure.in}, since it is derived from that file and from the public domain file @file{acconfig.h}. @file{config.sub} and @file{config.guess} have an exception to the GPL when they are used with an Autoconf-generated @code{configure} script, which permits you to distribute them under the same terms as the rest of your package. @file{install-sh} is from the X Consortium and is not copyrighted. @node Why GNU m4, Bootstrapping, Distributing, Questions @section Why Require GNU M4? @display Why does Autoconf require @sc{gnu} M4? @end display Many M4 implementations have hard-coded limitations on the size and number of macros that Autoconf exceeds. They also lack several builtin macros that it would be difficult to get along without in a sophisticated application like Autoconf, including: @example builtin indir patsubst __file__ __line__ @end example Autoconf requires version 1.4 or above of @sc{gnu} M4 because it uses frozen state files. Since only software maintainers need to use Autoconf, and since @sc{gnu} M4 is simple to configure and install, it seems reasonable to require @sc{gnu} M4 to be installed also. Many maintainers of @sc{gnu} and other free software already have most of the @sc{gnu} utilities installed, since they prefer them. @node Bootstrapping, Why Not Imake, Why GNU m4, Questions @section How Can I Bootstrap? @display If Autoconf requires @sc{gnu} M4 and @sc{gnu} M4 has an Autoconf @code{configure} script, how do I bootstrap? It seems like a chicken and egg problem! @end display This is a misunderstanding. Although @sc{gnu} M4 does come with a @code{configure} script produced by Autoconf, Autoconf is not required in order to run the script and install @sc{gnu} M4. Autoconf is only required if you want to change the M4 @code{configure} script, which few people have to do (mainly its maintainer). @node Why Not Imake, , Bootstrapping, Questions @section Why Not Imake? @display Why not use Imake instead of @code{configure} scripts? @end display Several people have written addressing this question, so I include adaptations of their explanations here. The following answer is based on one written by Richard Pixley: @quotation Autoconf generated scripts frequently work on machines that it has never been set up to handle before. That is, it does a good job of inferring a configuration for a new system. Imake cannot do this. Imake uses a common database of host specific data. For X11, this makes sense because the distribution is made as a collection of tools, by one central authority who has control over the database. @sc{gnu} tools are not released this way. Each @sc{gnu} tool has a maintainer; these maintainers are scattered across the world. Using a common database would be a maintenance nightmare. Autoconf may appear to be this kind of database, but in fact it is not. Instead of listing host dependencies, it lists program requirements. If you view the @sc{gnu} suite as a collection of native tools, then the problems are similar. But the @sc{gnu} development tools can be configured as cross tools in almost any host+target permutation. All of these configurations can be installed concurrently. They can even be configured to share host independent files across hosts. Imake doesn't address these issues. Imake templates are a form of standardization. The @sc{gnu} coding standards address the same issues without necessarily imposing the same restrictions. @end quotation Here is some further explanation, written by Per Bothner: @quotation One of the advantages of Imake is that it easy to generate large Makefiles using @code{cpp}'s @samp{#include} and macro mechanisms. However, @code{cpp} is not programmable: it has limited conditional facilities, and no looping. And @code{cpp} cannot inspect its environment. All of these problems are solved by using @code{sh} instead of @code{cpp}. The shell is fully programmable, has macro substitution, can execute (or source) other shell scripts, and can inspect its environment. @end quotation Paul Eggert elaborates more: @quotation With Autoconf, installers need not assume that Imake itself is already installed and working well. This may not seem like much of an advantage to people who are accustomed to Imake. But on many hosts Imake is not installed or the default installation is not working well, and requiring Imake to install a package hinders the acceptance of that package on those hosts. For example, the Imake template and configuration files might not be installed properly on a host, or the Imake build procedure might wrongly assume that all source files are in one big directory tree, or the Imake configuration might assume one compiler whereas the package or the installer needs to use another, or there might be a version mismatch between the Imake expected by the package and the Imake supported by the host. These problems are much rarer with Autoconf, where each package comes with its own independent configuration processor. Also, Imake often suffers from unexpected interactions between @code{make} and the installer's C preprocessor. The fundamental problem here is that the C preprocessor was designed to preprocess C programs, not @file{Makefile}s. This is much less of a problem with Autoconf, which uses the general-purpose preprocessor @code{m4}, and where the package's author (rather than the installer) does the preprocessing in a standard way. @end quotation Finally, Mark Eichin notes: @quotation Imake isn't all that extensible, either. In order to add new features to Imake, you need to provide your own project template, and duplicate most of the features of the existing one. This means that for a sophisticated project, using the vendor-provided Imake templates fails to provide any leverage---since they don't cover anything that your own project needs (unless it is an X11 program). On the other side, though: The one advantage that Imake has over @code{configure}: @file{Imakefile}s tend to be much shorter (likewise, less redundant) than @file{Makefile.in}s. There is a fix to this, however---at least for the Kerberos V5 tree, we've modified things to call in common @file{post.in} and @file{pre.in} @file{Makefile} fragments for the entire tree. This means that a lot of common things don't have to be duplicated, even though they normally are in @code{configure} setups. @end quotation @c ===================================================== History of Autoconf. @node History, Environment Variable Index, Questions, Top @chapter History of Autoconf You may be wondering, Why was Autoconf originally written? How did it get into its present form? (Why does it look like gorilla spit?) If you're not wondering, then this chapter contains no information useful to you, and you might as well skip it. If you @emph{are} wondering, then let there be light@dots{} @menu * Genesis:: Prehistory and naming of @code{configure} * Exodus:: The plagues of M4 and Perl * Leviticus:: The priestly code of portability arrives * Numbers:: Growth and contributors * Deuteronomy:: Approaching the promises of easy configuration @end menu @node Genesis, Exodus, History, History @section Genesis In June 1991 I was maintaining many of the @sc{gnu} utilities for the Free Software Foundation. As they were ported to more platforms and more programs were added, the number of @option{-D} options that users had to select in the @file{Makefile} (around 20) became burdensome. Especially for me---I had to test each new release on a bunch of different systems. So I wrote a little shell script to guess some of the correct settings for the fileutils package, and released it as part of fileutils 2.0. That @code{configure} script worked well enough that the next month I adapted it (by hand) to create similar @code{configure} scripts for several other @sc{gnu} utilities packages. Brian Berliner also adapted one of my scripts for his @sc{cvs} revision control system. Later that summer, I learned that Richard Stallman and Richard Pixley were developing similar scripts to use in the @sc{gnu} compiler tools; so I adapted my @code{configure} scripts to support their evolving interface: using the file name @file{Makefile.in} as the templates; adding @samp{+srcdir}, the first option (of many); and creating @file{config.status} files. @node Exodus, Leviticus, Genesis, History @section Exodus As I got feedback from users, I incorporated many improvements, using Emacs to search and replace, cut and paste, similar changes in each of the scripts. As I adapted more @sc{gnu} utilities packages to use @code{configure} scripts, updating them all by hand became impractical. Rich Murphey, the maintainer of the @sc{gnu} graphics utilities, sent me mail saying that the @code{configure} scripts were great, and asking if I had a tool for generating them that I could send him. No, I thought, but I should! So I started to work out how to generate them. And the journey from the slavery of hand-written @code{configure} scripts to the abundance and ease of Autoconf began. Cygnus @code{configure}, which was being developed at around that time, is table driven; it is meant to deal mainly with a discrete number of system types with a small number of mainly unguessable features (such as details of the object file format). The automatic configuration system that Brian Fox had developed for Bash takes a similar approach. For general use, it seems to me a hopeless cause to try to maintain an up-to-date database of which features each variant of each operating system has. It's easier and more reliable to check for most features on the fly---especially on hybrid systems that people have hacked on locally or that have patches from vendors installed. I considered using an architecture similar to that of Cygnus @code{configure}, where there is a single @code{configure} script that reads pieces of @file{configure.in} when run. But I didn't want to have to distribute all of the feature tests with every package, so I settled on having a different @code{configure} made from each @file{configure.in} by a preprocessor. That approach also offered more control and flexibility. I looked briefly into using the Metaconfig package, by Larry Wall, Harlan Stenn, and Raphael Manfredi, but I decided not to for several reasons. The @code{Configure} scripts it produces are interactive, which I find quite inconvenient; I didn't like the ways it checked for some features (such as library functions); I didn't know that it was still being maintained, and the @code{Configure} scripts I had seen didn't work on many modern systems (such as System V R4 and NeXT); it wasn't very flexible in what it could do in response to a feature's presence or absence; I found it confusing to learn; and it was too big and complex for my needs (I didn't realize then how much Autoconf would eventually have to grow). I considered using Perl to generate my style of @code{configure} scripts, but decided that M4 was better suited to the job of simple textual substitutions: it gets in the way less, because output is implicit. Plus, everyone already has it. (Initially I didn't rely on the @sc{gnu} extensions to M4.) Also, some of my friends at the University of Maryland had recently been putting M4 front ends on several programs, including @code{tvtwm}, and I was interested in trying out a new language. @node Leviticus, Numbers, Exodus, History @section Leviticus Since my @code{configure} scripts determine the system's capabilities automatically, with no interactive user intervention, I decided to call the program that generates them Autoconfig. But with a version number tacked on, that name would be too long for old @sc{unix} file systems, so I shortened it to Autoconf. In the fall of 1991 I called together a group of fellow questers after the Holy Grail of portability (er, that is, alpha testers) to give me feedback as I encapsulated pieces of my handwritten scripts in M4 macros and continued to add features and improve the techniques used in the checks. Prominent among the testers were Fran@,cois Pinard, who came up with the idea of making an @file{autoconf} shell script to run @code{m4} and check for unresolved macro calls; Richard Pixley, who suggested running the compiler instead of searching the file system to find include files and symbols, for more accurate results; Karl Berry, who got Autoconf to configure @TeX{} and added the macro index to the documentation; and Ian Lance Taylor, who added support for creating a C header file as an alternative to putting @option{-D} options in a @file{Makefile}, so he could use Autoconf for his @sc{uucp} package. The alpha testers cheerfully adjusted their files again and again as the names and calling conventions of the Autoconf macros changed from release to release. They all contributed many specific checks, great ideas, and bug fixes. @node Numbers, Deuteronomy, Leviticus, History @section Numbers In July 1992, after months of alpha testing, I released Autoconf 1.0, and converted many @sc{gnu} packages to use it. I was surprised by how positive the reaction to it was. More people started using it than I could keep track of, including people working on software that wasn't part of the @sc{gnu} Project (such as TCL, FSP, and Kerberos V5). Autoconf continued to improve rapidly, as many people using the @code{configure} scripts reported problems they encountered. Autoconf turned out to be a good torture test for M4 implementations. @sc{unix} @code{m4} started to dump core because of the length of the macros that Autoconf defined, and several bugs showed up in @sc{gnu} @code{m4} as well. Eventually, we realized that we needed to use some features that only @sc{gnu} M4 has. 4.3@sc{bsd} @code{m4}, in particular, has an impoverished set of builtin macros; the System V version is better, but still doesn't provide everything we need. More development occurred as people put Autoconf under more stresses (and to uses I hadn't anticipated). Karl Berry added checks for X11. david zuhn contributed C++ support. Fran@,cois Pinard made it diagnose invalid arguments. Jim Blandy bravely coerced it into configuring @sc{gnu} Emacs, laying the groundwork for several later improvements. Roland McGrath got it to configure the @sc{gnu} C Library, wrote the @code{autoheader} script to automate the creation of C header file templates, and added a @option{--verbose} option to @code{configure}. Noah Friedman added the @option{--autoconf-dir} option and @code{AC_MACRODIR} environment variable. (He also coined the term @dfn{autoconfiscate} to mean ``adapt a software package to use Autoconf''.) Roland and Noah improved the quoting protection in @code{AC_DEFINE} and fixed many bugs, especially when I got sick of dealing with portability problems from February through June, 1993. @node Deuteronomy, , Numbers, History @section Deuteronomy A long wish list for major features had accumulated, and the effect of several years of patching by various people had left some residual cruft. In April 1994, while working for Cygnus Support, I began a major revision of Autoconf. I added most of the features of the Cygnus @code{configure} that Autoconf had lacked, largely by adapting the relevant parts of Cygnus @code{configure} with the help of david zuhn and Ken Raeburn. These features include support for using @file{config.sub}, @file{config.guess}, @option{--host}, and @option{--target}; making links to files; and running @code{configure} scripts in subdirectories. Adding these features enabled Ken to convert @sc{gnu} @code{as}, and Rob Savoye to convert DejaGNU, to using Autoconf. I added more features in response to other peoples' requests. Many people had asked for @code{configure} scripts to share the results of the checks between runs, because (particularly when configuring a large source tree, like Cygnus does) they were frustratingly slow. Mike Haertel suggested adding site-specific initialization scripts. People distributing software that had to unpack on MS-DOS asked for a way to override the @file{.in} extension on the file names, which produced file names like @file{config.h.in} containing two dots. Jim Avera did an extensive examination of the problems with quoting in @code{AC_DEFINE} and @code{AC_SUBST}; his insights led to significant improvements. Richard Stallman asked that compiler output be sent to @file{config.log} instead of @file{/dev/null}, to help people debug the Emacs @code{configure} script. I made some other changes because of my dissatisfaction with the quality of the program. I made the messages showing results of the checks less ambiguous, always printing a result. I regularized the names of the macros and cleaned up coding style inconsistencies. I added some auxiliary utilities that I had developed to help convert source code packages to use Autoconf. With the help of Fran@,cois Pinard, I made the macros not interrupt each others' messages. (That feature revealed some performance bottlenecks in @sc{gnu} @code{m4}, which he hastily corrected!) I reorganized the documentation around problems people want to solve. And I began a test suite, because experience had shown that Autoconf has a pronounced tendency to regress when we change it. Again, several alpha testers gave invaluable feedback, especially Fran@,cois Pinard, Jim Meyering, Karl Berry, Rob Savoye, Ken Raeburn, and Mark Eichin. Finally, version 2.0 was ready. And there was much rejoicing. (And I have free time again. I think. Yeah, right.) @c ========================================================== Appendices @node Environment Variable Index, Output Variable Index, History, Top @unnumbered Environment Variable Index This is an alphabetical list of the environment variables that Autoconf checks. @printindex ev @node Output Variable Index, Preprocessor Symbol Index, Environment Variable Index, Top @unnumbered Output Variable Index This is an alphabetical list of the variables that Autoconf can substitute into files that it creates, typically one or more @file{Makefile}s. @xref{Setting Output Variables}, for more information on how this is done. @printindex ov @node Preprocessor Symbol Index, Macro Index, Output Variable Index, Top @unnumbered Preprocessor Symbol Index This is an alphabetical list of the C preprocessor symbols that the Autoconf macros define. To work with Autoconf, C source code needs to use these names in @code{#if} directives. @printindex cv @node Macro Index, Concept Index, Preprocessor Symbol Index, Top @unnumbered Macro Index This is an alphabetical list of the Autoconf macros. To make the list easier to use, the macros are listed without their preceding @samp{AC_}. @printindex ma @node Concept Index, , Macro Index, Top @unnumbered Concept Index @c FIXME: Find some nice wording to introduce this section. @printindex cp @contents @bye @c Local Variables: @c ispell-local-dictionary: "american" @c End: