\input texinfo @c -*-texinfo-*- @c %**start of header @setfilename autoconf.info @settitle Autoconf @c For double-sided printing, uncomment: @c @setchapternewpage odd @c %**end of header @set EDITION 1.117 @set VERSION 1.117 @set UPDATED September 1994 @iftex @finalout @end iftex @ifinfo @format START-INFO-DIR-ENTRY * Autoconf: (autoconf). Create source code configuration scripts. END-INFO-DIR-ENTRY @end format 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 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 by David MacKenzie @c I think I've rewritten all of Noah and Roland's contributions by now. @page @vskip 0pt plus 1filll Copyright @copyright{} 1992, 1993, 1994 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) @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 an @code{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. * 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}. * Invoking configure:: How to use the Autoconf output. * Invoking config.status:: Recreating a configuration. * Concerns:: Concerns about Autoconf, with answers. * Upgrading:: Tips for upgrading from version 1. * History:: History of Autoconf. * Old Macro Names:: Backward compatibility macros. * 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. --- The Detailed Node Listing --- Making @code{configure} Scripts * Writing configure.in:: What to put in an Autoconf input file. * Invoking autoscan:: Semi-automatic @file{configure.in} writing. * Invoking ifnames:: Listing the conditionals in source code. * Invoking autoconf:: How to create configuration scripts. * Invoking autoreconf:: Remaking multiple @code{configure} scripts. Initialization and Output Files * Input:: Where Autoconf should find files. * Output:: Creating output files. * Makefile Substitutions:: Using output variables in @file{Makefile}s. * Configuration Headers:: Creating a configuration header file. * Subdirectories:: Configuring independent packages together. * Versions:: Version numbers in @code{configure}. Substitutions in Makefiles * Preset Output Variables:: Output variables that are always set. * Build Directories:: Compiling in a different directory. * Automatic Remaking:: Makefile rules for configuring. Configuration Header Files * Header Templates:: Input for the configuration headers. * Invoking autoheader:: How to create configuration templates. Existing Tests * 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. * Structures:: Structures or members that might be missing. * Typedefs:: @code{typedef}s that might be missing. * Compiler Characteristics:: C compiler or machine architecture features. * System Services:: Operating system services. * UNIX Variants:: Special kludges for specific UNIX variants. 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. Typedefs * Particular Typedefs:: Special handling to find certain types. * Generic Typedefs:: How to find other types. Writing Tests * Examining Declarations:: Detecting header files and declarations. * Examining Libraries:: Detecting functions and global variables. * Run Time:: Testing for run-time features. * Portable Shell:: Shell script portability pitfalls. * Testing Values and Files:: Checking strings and files. * 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. 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 users of progress or problems. 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. * Dependencies Between Macros:: What to do when macros depend on other macros. Dependencies Between Macros * Prerequisite Macros:: Ensuring required information. * Suggested Ordering:: Warning about possible ordering problems. * Obsolete Macros:: Warning about old ways of doing things. Manual Configuration * Specifying Names:: Specifying the system type. * Canonicalizing:: Getting the canonical system type. * System Type Variables:: Variables containing the 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. * Site Details:: Configuring site details. * Transforming Names:: Changing program names when installing. * Site Defaults:: Giving @code{configure} local defaults. Running @code{configure} Scripts * Basic Installation:: Instructions for typical cases. * Compilers and Options:: Selecting compilers and optimization. * Build Directory:: Configuring in a different directory. * Installation Names:: Installing in different directories. * System Type:: Specifying the system type. * Optional Features:: Selecting optional features. Concerns About Autoconf * Copyright:: Legal restrictions on Autoconf output. * Why GNU m4:: Why not use the standard @code{m4}? * Bootstrapping:: Autoconf and GNU @code{m4} require each other? 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. * Invoking autoupdate:: Replacing old macro names in @code{configure.in}. * Changed Results:: Changes in how to check test results. * Changed Macro Writing:: Better ways to write your own macros. History of Autoconf * Genesis:: Prehistory and naming of @code{configure}. * Exodus:: The plagues of @code{m4} and Perl. * Leviticus:: The priestly code of portability arrives. * Numbers:: Growth and contributors. * Deuteronomy:: Approaching the promises of easy configuration. @end menu @node Introduction, Making configure Scripts, Top, Top @chapter Introduction @display 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 display @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 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 test for the presence of each feature that the software package they are for might need individually. (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 UNIX variants. There is no need to maintain files that list the features supported by each release of each variant of 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. Larry Wall's 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. Autoconf imposes some restrictions on the names of macros used with @code{#ifdef} in C programs (@pxref{Preprocessor Symbol Index}). Autoconf requires GNU @code{m4} in order to generate the scripts. It uses features that some UNIX versions of @code{m4} do not have. It also overflows internal limits of some versions of @code{m4}, including GNU @code{m4} 1.0. You must use version 1.1 or later of GNU @code{m4}. Using version 1.3 or later will be much faster than 1.1 or 1.2. @xref{Upgrading}, for information about upgrading from version 1. @xref{History}, for the story of Autoconf's development. @xref{Concerns}, for answers to some common questions about Autoconf. Mail suggestions and bug reports for Autoconf to @code{bug-gnu-utils@@prep.ai.mit.edu}. Please include the Autoconf version number, which you can get by running @samp{autoconf --version}. @node Making configure Scripts, Setup, Introduction, Top @chapter Making @code{configure} Scripts 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{Invoking config.status}); @item a shell script called @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 write @file{acconfig.h}, and you will distribute the Autoconf-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. * Invoking autoscan:: Semi-automatic @file{configure.in} writing. * Invoking ifnames:: Listing the conditionals in source code. * Invoking autoconf:: How to create configuration scripts. * Invoking autoreconf:: Remaking multiple @code{configure} scripts. @end menu @node Writing configure.in, Invoking autoscan, , 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{Invoking autoscan}, for more information). 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. @display @group @code{AC_INIT(@var{file})} checks for alternative programs checks for libraries checks for header files checks for typedefs checks for library functions checks for structures checks for compiler characteristics checks for system services @code{AC_OUTPUT(@r{[}@var{file@dots{}}@r{]})} @end group @end display When calling macros that take arguments, there must not be any blank space between the macro name and the open parenthesis. Arguments can be more than one line long if they are enclosed within the @code{m4} quote characters @samp{[} and @samp{]}. Some macros handle two cases: what to do if the given condition is met, and what to do if the condition is not met. In some places you might want to do something if a condition is true but do nothing if it's false, or vice versa. To omit the true case, pass an empty value for the @var{action-if-found} argument to the macro. To omit the false case, omit the @var{action-if-not-found} argument to the macro, including the comma before it. You can include comments in @file{configure.in} files by starting them with the @code{m4} predefined macro @code{dnl}, which discards text up through the next newline. These comments do not appear in the generated @code{configure} scripts. For example, it is helpful to begin @file{configure.in} files with a line like this: @example dnl Process this file with autoconf to produce a configure script. @end example @node Invoking autoscan, Invoking ifnames, Writing configure.in, Making configure Scripts @section Using @code{autoscan} to Create @file{configure.in} 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. For example, if you want the package to use a configuration header file, you will have to add a call to @code{AC_CONFIG_HEADER} (@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{Invoking ifnames}, 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 @code @item --help Print a summary of the command line options and exit. @item --macrodir=@var{dir} @evindex AC_MACRODIR Look for the data files in directory @var{dir} instead of the default installation directory. You can also set the @code{AC_MACRODIR} environment variable to a directory; this option overrides the environment variable. @item --verbose Print the names of the files it examines and the potentially interesting symbols it finds in them. This output can be voluminous. @item --version Print the version number of Autoconf and exit. @end table @node Invoking ifnames, Invoking autoconf, Invoking autoscan, Making configure Scripts @section Using @code{ifnames} to List Conditionals @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{Invoking autoscan}). @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}, or @code{#ifdef} 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 @code @item --help Print a summary of the command line options and exit. @item --macrodir=@var{dir} @evindex AC_MACRODIR Look for the Autoconf macro files in directory @var{dir} instead of the default installation directory. Only used to get the version number. You can also set the @code{AC_MACRODIR} environment variable to a directory; this option overrides the environment variable. @item --version Print the version number of Autoconf and exit. @end table @node Invoking autoconf, Invoking autoreconf, Invoking ifnames, Making configure Scripts @section Using @code{autoconf} to Create @code{configure} 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 @samp{-}, 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 @code @item --help Print a summary of the command line options and exit. @item --macrodir=@var{dir} @evindex AC_MACRODIR Look for the installed macro files in directory @var{dir}. You can also set the @code{AC_MACRODIR} environment variable to a directory; this option overrides the environment variable. @item --version Print the version number of Autoconf and exit. @end table @node Invoking autoreconf, , Invoking autoconf, Making configure Scripts @section Using @code{autoreconf} to Update @code{configure} Scripts If you have a lot of Autoconf-generated @code{configure} scripts and you get a new version of Autoconf, the @code{autoreconf} program can be handy. It runs @code{autoconf} (and @code{autoheader}, where appropriate) repeatedly to remake all of the Autoconf @code{configure} scripts in a directory tree. @xref{Automatic Remaking}, for further information about automatic remaking of @code{configure} scripts. @noindent @code{autoreconf} accepts the following options: @table @code @item --help @itemx -h Print a summary of the command line options and exit. @item --macrodir=@var{dir} @itemx -m @var{dir} @evindex AC_MACRODIR Look for the Autoconf macro files in directory @var{dir} instead of the default installation directory. You can also set the @code{AC_MACRODIR} environment variable to a directory; this option overrides the environment variable. @item --verbose Print the name of each directory where @code{autoreconf} runs @code{autoconf} (and @code{autoheader}, if that directory's @file{configure.in} calls @code{AC_CONFIG_HEADER}). @item --version Print the version number of Autoconf and exit. @end table @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 * Input:: Where Autoconf should find files. * Output:: Creating output files. * Makefile Substitutions:: Using output variables in @file{Makefile}s. * Configuration Headers:: Creating a configuration header file. * Subdirectories:: Configuring independent packages together. * Versions:: Version numbers in @code{configure}. @end menu @node Input, Output, , 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{unique-file-in-source-dir}) @maindex INIT Process any command-line arguments and find the source code directory. @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 (@pxref{Invoking configure}, for more information). @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, Makefile Substitutions, Input, Setup @section Creating Output Files Every Autoconf-generated @code{configure} script must finish by calling @code{AC_OUTPUT}. It is the macro that creates the @file{Makefile}s and optional other files resulting from configuration. The only other required macro is @code{AC_INIT} (@pxref{Input}). @defmac AC_OUTPUT (@r{[}@var{file}@dots{}@r{] [,}@var{extra-cmds}@r{] [,}@var{init-cmds}@r{]}) @maindex OUTPUT Create output files. The @var{file}@dots{} argument is a whitespace-separated list of output files; it may be empty. This macro creates each file @file{@var{file}} by copying an input file (by default named @file{@var{file}.in}), substituting the output variable values. @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 (but not the parents of that directory). Usually, @file{Makefile}s are created this way, but other files, such as @file{.gdbinit}, can be specified as well. If @code{AC_CONFIG_HEADER}, @code{AC_LINK_FILES}, or @code{AC_CONFIG_SUBDIRS} has been called, this macro also creates the files named as their arguments. A typical call to @code{AC_OUTPUT} looks like this: @example AC_OUTPUT(Makefile src/Makefile man/Makefile X/Imakefile) @end example You can override an input file name by appending it to @var{file}, separated by a colon. For example, @example AC_OUTPUT(Makefile:templates/top.mk lib/Makefile:templates/lib.mk) @end example If you pass @var{extra-cmds}, those commands will be inserted into @file{config.status} to be run after all its other processing. If @var{init-cmds} are given, they are inserted just before @var{extra-cmds}, with shell variable, command, and backslash substitutions performed on them in @code{configure}. You can use @var{init-cmds} to pass variables from @code{configure} to the @var{extra-cmds}. @end defmac @node Makefile Substitutions, Configuration Headers, Output, 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.info, 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. * Build Directories:: Compiling in a different directory. * Automatic Remaking:: Makefile rules for configuring. @end menu @node Preset Output Variables, Build Directories, , 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. @defvar exec_prefix @ovindex exec_prefix The installation prefix for architecture-specific files. @end defvar @defvar prefix @ovindex prefix The installation prefix for architecture-independent files. @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 @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 CPPFLAGS @ovindex CPPFLAGS Header file search directory (@samp{-I@var{dir}}) and any other miscellaneous options for the C preprocessor and compiler. 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 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 @samp{-D} options to pass to the C compiler. If @code{AC_CONFIG_HEADER} is called, @code{configure} replaces @samp{@@DEFS@@} with @samp{-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 LDFLAGS @ovindex LDFLAGS Stripping (@samp{-s}) and any other miscellaneous options for the linker. 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 features. @end defvar @defvar LIBS @ovindex LIBS @samp{-l} and @samp{-L} options to pass to the linker. @end defvar @node Build Directories, Automatic Remaking, Preset Output Variables, Makefile Substitutions @subsection Build Directories You might want to compile a software package in a different directory from the one that contains the source code. Doing this allows you to compile the package for several architectures simultaneously from the same copy of the source code and keep multiple sets of object files on disk. To support doing this, @code{make} uses the @code{VPATH} variable to find the files that are in the source directory. 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 = $(srcdir)}, because some versions of @code{make} do not do variable substitutions on the value of @code{VPATH}. @code{configure} substitutes in the correct value for @code{srcdir} when it produces @file{Makefile.in}. Do not use the @code{make} variable @code{$<}, which expands to the pathname 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 any of these files that your package does not use. 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 BSD systems, @code{touch} or any command that results in an empty file does not update the timestamps, so use a command like @code{date} as a workaround. @example @group configure: configure.in aclocal.m4 cd $@{srcdir@} && autoconf # autoheader might not change config.h.in, so touch a stamp file. config.h.in: stamp-h.in stamp-h.in: configure.in aclocal.m4 acconfig.h config.h.top config.h.bot cd $@{srcdir@} && autoheader date > $@{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 pass @samp{date > stamp-h} in the @var{extra-cmds} argument to @code{AC_OUTPUT}, 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{Invoking config.status}, for more examples of handling configuration-related dependencies. @node Configuration Headers, Subdirectories, Makefile Substitutions, Setup @section Configuration Header Files When a package tests more than a few C preprocessor symbols, the command lines to pass @samp{-D} options to the compiler can get quite long. This causes two problems. One is that the @code{make} output is hard to read. More seriously, the command lines can exceed the length limits of some operating systems. As an alternative to passing @samp{-D} options to the compiler, @code{configure} scripts can create a C header file containing @samp{#define} directives. The @code{AC_CONFIG_HEADER} 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. @defmac AC_CONFIG_HEADER (@var{header-to-create} @dots{}) @maindex CONFIG_HEADER @cvindex HAVE_CONFIG_H Make @code{AC_OUTPUT} create the file(s) in the whitespace-separated list @var{header-to-create} containing C preprocessor @code{#define} statements, and replace @samp{@@DEFS@@} in generated files with @samp{-DHAVE_CONFIG_H} instead of the value of @code{DEFS}. The usual name for @var{header-to-create} is @file{config.h}. If @var{header-to-create} 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-to-create}.in}; however, you can override the input file name by appending it to @var{header-to-create}, separated by a colon. For example, @example AC_CONFIG_HEADER(defines.h:defines.hin) @end example @noindent Doing this allows you to keep your filenames acceptable to MS-DOS. @end defmac @menu * Header Templates:: Input for the configuration headers. * Invoking autoheader:: How to create configuration templates. @end menu @node Header Templates, Invoking autoheader, , Configuration Headers @subsection Configuration Header Templates Your distribution should contain a template file that looks as you want the final header file to look, including comments, with default values in the @code{#define} statements. For example, suppose your @file{configure.in} makes these calls: @example AC_CONFIG_HEADER(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 change the 0 to a 1. On other systems, it will leave the line unchanged. @example @group /* Define as 1 if you have unistd.h. */ #define HAVE_UNISTD_H 0 @end group @end example Alternately, if your code tests for configuration options using @code{#ifdef} instead of @code{#if}, a default value can be to @code{#undef} the variable instead of to define it to a value. On systems that have @file{unistd.h}, @code{configure} will change the second line to read @samp{#define HAVE_UNISTD_H 1}. On other systems, it will comment that line out (in case the system predefines that symbol). @example @group /* Define if you have unistd.h. */ #undef HAVE_UNISTD_H @end group @end example @node Invoking autoheader, , Header Templates, Configuration Headers @subsection Using @code{autoheader} to Create @file{config.h.in} The @code{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_HEADER(@var{file})}, @code{autoheader} creates @file{@var{file}.in}. Otherwise, @code{autoheader} creates @file{config.h.in}. If you give @code{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 @code{autoheader} an argument of @samp{-}, it reads the standard input instead of @file{configure.in} and writes the header file to the standard output. @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}, which comes with and is installed with Autoconf. It also uses a file called @file{acconfig.h} in the current directory, if present. If you @code{AC_DEFINE} any additional symbols, you must create that file with entries for them. For symbols defined by @code{AC_CHECK_HEADERS}, @code{AC_CHECK_FUNCS}, @code{AC_CHECK_SIZEOF}, or @code{AC_CHECK_LIB}, @code{autoheader} generates comments and @code{#undef} statements itself rather than copying them from a file, since the possible symbols are effectively limitless. 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 obsolete 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 can not be stored on MS-DOS; also, they are two more files to clutter up the directory. @code{autoheader} accepts the following options: @table @code @item --help Print a summary of the command line options and exit. @item --macrodir=@var{dir} @evindex AC_MACRODIR Look for the installed macro files and @file{acconfig.h} in directory @var{dir}. You can also set the @code{AC_MACRODIR} environment variable to a directory; this option overrides the environment variable. @item --version Print the version number of Autoconf and exit. @end table @node Subdirectories, Versions, Configuration Headers, 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. 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 @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. @end defmac @node Versions, , Subdirectories, Setup @section Version Numbers in @code{configure} The following macros manage version numbers for @code{configure} scripts. Using them is optional. @defmac AC_PREREQ (@var{version}) @maindex PREREQ 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(1.8) @end example This macro is useful if your @file{configure.in} relies on non-obvious behavior that changed between Autoconf releases. If it merely needs recently added macros, then @code{AC_PREREQ} is less useful, because the @code{autoconf} program already tells the user which macros are not found. The same thing happens if @file{configure.in} is processed by a version of Autoconf older than when @code{AC_PREREQ} was added. @end defmac @defmac AC_REVISION (@var{revision-info}) @maindex 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 RCS or 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. It is a good idea to call this macro before @code{AC_INIT} so that the revision number is near the top of both @file{configure.in} and @code{configure}. To support doing that, the @code{AC_REVISION} output begins with @samp{#!/bin/sh}, like the normal start of a @code{configure} script does. 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 }$)dnl @end example @noindent produces this in @code{configure}: @example #!/bin/sh # From configure.in Revision: 1.30 @end example @end defmac @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{Setting Output Variables}, for details on how this is done. The phrase ``define @var{name}'' is used below as a shorthand to mean ``define C preprocessor symbol @var{name} to have the value 1''. @menu * 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. * Structures:: Structures or members that might be missing. * Typedefs:: @code{typedef}s that might be missing. * Compiler Characteristics:: C compiler or machine architecture features. * System Services:: Operating system services. * UNIX Variants:: Special kludges for specific UNIX variants. @end menu @node Alternative Programs, Libraries, , Existing Tests @section Alternative Programs 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 @subsection Particular Program Checks These macros check for particular programs---whether they exist, and in some cases whether they support certain features. @defmac AC_DECL_YYTEXT @maindex DECL_YYTEXT @cvindex YYTEXT_POINTER @ovindex LEX_OUTPUT_ROOT 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. @end defmac @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 it finds. It tries @code{mawk} first because that is reported to be the fastest implementation. @end defmac @defmac AC_PROG_CC @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 use @code{cc} if it's not found. Set output variable @code{CC} to the name of the compiler found. If using the GNU C compiler, set shell variable @code{GCC} to @samp{yes}, empty otherwise. If output variable @code{CFLAGS} was not already set, set it to @samp{-g -O} for the GNU C compiler (@samp{-O} on systems where GCC does not accept @samp{-g}), or @samp{-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 @samp{-c} and @samp{-o} options simultaneously, define @code{NO_MINUS_C_MINUS_O}. @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, it uses @file{/lib/cpp}. 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}. @end defmac @defmac AC_PROG_CXX @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, set output variable @code{CXX} to its value. Otherwise search for a C++ compiler under likely names (@code{c++}, @code{g++}, @code{gcc}, @code{CC}, and @code{cxx}). If none of those checks succeed, as a last resort set @code{CXX} to @code{gcc}. If using the GNU C++ compiler, set shell variable @code{GXX} to @samp{yes}, empty otherwise. If output variable @code{CXXFLAGS} was not already set, set it to @samp{-g -O} for the GNU C++ compiler (@samp{-O} on systems where G++ does not accept @samp{-g}), or @samp{-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{$CXX -E} doesn't work, it uses @file{/lib/cpp}. It is only portable to run @code{CXXCPP} on files with a @file{.c}, @file{.C}, or @file{.cc} extension. If the current language is C++ (@pxref{Language Choice}), many of the specific test macros use the value of @code{CXXCPP} indirectly by calling @code{AC_TRY_CPP}, @code{AC_CHECK_HEADER}, @code{AC_EGREP_HEADER}, or @code{AC_EGREP_CPP}. @end defmac @defmac AC_PROG_GCC_TRADITIONAL @maindex PROG_GCC_TRADITIONAL @ovindex CC Add @samp{-traditional} to output variable @code{CC} if using the GNU C compiler and @code{ioctl} does not work properly without @samp{-traditional}. That usually happens when the fixed header files have not been installed on an old system. Since recent versions of the GNU C compiler fix the header files automatically when installed, this is becoming a less prevalent problem. @end defmac @defmac AC_PROG_INSTALL @maindex PROG_INSTALL @ovindex INSTALL @ovindex INSTALL_PROGRAM @ovindex INSTALL_DATA Set output variable @code{INSTALL} to the path of a BSD compatible @code{install} program, if one is found in the current @code{PATH}. Otherwise, set @code{INSTALL} to @samp{@var{dir}/install-sh -c}, checking the directories specified to @code{AC_CONFIG_AUX_DIR} (or its default directories) to determine @var{dir} (@pxref{Output}). Also set the variable @code{INSTALL_PROGRAM} to @samp{$@{INSTALL@}} and @code{INSTALL_DATA} to @samp{$@{INSTALL@} -m 644}. This macro screens out various instances of @code{install} known to not 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}. 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 pathname of your program into your @file{Makefile.in} files. @end defmac @defmac AC_PROG_LEX @maindex PROG_LEX @ovindex LEX @ovindex LEXLIB If @code{flex} is found, set output variable @code{LEX} to @samp{flex} and @code{LEXLIB} to @samp{-lfl}, if that library is in a standard place. Otherwise set @code{LEX} to @samp{lex} and @code{LEXLIB} to @samp{-ll}. @end defmac @defmac AC_PROG_LN_S @maindex PROG_LN_S @ovindex LN_S If @samp{ln -s} works on the current filesystem (the operating system and filesystem support symbolic links), set output variable @code{LN_S} to @samp{ln -s}, otherwise set it to @samp{ln}. @end defmac @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}. In recent versions of @code{make}, the variable @code{MAKE} contains the name of the @code{make} program plus options it was given. It is used when running @code{make} recursively in subdirectories. But some old versions of @code{make} don't set the @code{MAKE} variable. This macro allows use of @code{MAKE} on all systems. If you use this macro, simply place a line like this in your @file{Makefile.in} file(s): @example @@SET_MAKE@@ @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 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}). @defmac AC_CHECK_PROG (@var{variable}, @var{prog-to-check-for}, @var{value-if-found} @r{[}, @var{value-if-not-found}@r{]}) @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. 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} @r{[}, @var{value-if-not-found}@r{]}) @maindex CHECK_PROGS Check for each program in the whitespace-separated list @var{progs-to-check-for} exists in @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_PATH_PROG (@var{variable}, @var{prog-to-check-for} @r{[}, @var{value-if-not-found}@r{]}) @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} @r{[}, @var{value-if-not-found}@r{]}) @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_PREFIX_PROGRAM (@var{program}) @maindex PREFIX_PROGRAM If the user did not specify an installation prefix (using the @samp{--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 @node Libraries, Library Functions, Alternative Programs, Existing Tests @section Library Files The following macros check for the presence of certain C library archive files. @defmac AC_CHECK_LIB (@var{library}, @var{function}, @r{[}, @var{action-if-found} @r{[}, @var{action-if-not-found} @r{[}, @var{other-libraries}@r{]]]}) @maindex CHECK_LIB See whether a test C program can be linked with the library @var{library}. @var{function} should be the name of a function that the library contains, to force the linker to try to link with the library to resolve the name. @var{library} is the base name of the library; e.g., to check for @samp{-lmp}, use @samp{mp} as the @var{library} argument. @var{action-if-found} is a list of shell commands to run if the link succeeds (which means that the library is present); @var{action-if-not-found} is a list of shell commands to run if the link fails. If @var{action-if-found} and @var{action-if-not-found} are not specified, the default action is to add @samp{-l@var{library}} to @code{LIBS} and define @samp{HAVE_LIB@var{library}}. 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: @samp{-lX11 -lXt}. Otherwise this macro will fail to detect that @var{library} is present, because linking the test program will always fail with unresolved symbols. @end defmac @defmac AC_HAVE_LIBRARY (@var{library}, @r{[}, @var{action-if-found} @r{[}, @var{action-if-not-found} @r{[}, @var{other-libraries}@r{]]]}) @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}, @samp{-lfoo}, or @samp{libfoo.a}. In all of those cases, the compiler is passed @samp{-lfoo}. However, @var{library} can not be a shell variable; it must be a literal name. This macro is considered obsolete. @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 @subsection Particular Function Checks 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-ANSI C compilers will ignore it, rather than choke on it. @example @group /* AIX requires this to be the first thing in the file. */ #ifdef __GNUC__ # define alloca __builtin_alloca #else # 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_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_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 @ovindex LIBOBJS @ovindex NEED_SETGID @ovindex KMEM_GROUP Check how to get the system load averages. If the system has the @code{getloadavg} function, this macro defines @code{HAVE_GETLOADAVG}, and adds to @code{LIBS} any libraries needed to get that function. Otherwise, it adds @samp{getloadavg.o} to the output variable @code{LIBOBJS}, and possibly defines several other C preprocessor macros and output variables: @enumerate @item It defines @code{SVR4}, @code{DGUX}, @code{UMAX}, or @code{UMAX4_3} if on those systems. @item If it finds @file{nlist.h}, it defines @code{NLIST_STRUCT}. @item If @samp{struct nlist} has an @samp{n_un} member, it defines @code{NLIST_NAME_UNION}. @item If compiling @file{getloadavg.c} defines @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 the @code{getmntent} in the @file{sun} and @file{seq} libraries, for Irix 4 and PTX, respectively. Then, if @code{getmntent} is available, define @code{HAVE_GETMNTENT}. @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), add @samp{memcmp.o} to output variable @code{LIBOBJS}. @end defmac @defmac AC_FUNC_MMAP @maindex FUNC_MMAP @cvindex HAVE_MMAP If the @code{mmap} function exists and works correctly on memory mapped files, define @code{HAVE_MMAP}. @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}. This is the case on System V before release 3. @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}, which should not be used. @end defmac @defmac AC_FUNC_STRFTIME @maindex FUNC_STRFTIME @cvindex HAVE_STRFTIME Check for @code{strftime} in the @file{intl} library, for SCO 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. @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}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]}) @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_CPLUSPLUS} 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{} @r{[}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]]}) @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 caps). 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 @defmac AC_REPLACE_FUNCS (@var{function-name}@dots{}) @maindex REPLACE_FUNCS @ovindex LIBOBJS For each given @var{function-name} in the whitespace-separated argument list that is not in the C library, add @samp{@var{function-name}.o} to the value of the output variable @code{LIBOBJS}. @end defmac @node Header Files, Structures, Library Functions, Existing Tests @section Header Files 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 @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_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 @defmac AC_DIR_HEADER @maindex DIR_HEADER @cvindex DIRENT @cvindex SYSDIR @cvindex SYSNDIR @cvindex NDIR @cvindex VOID_CLOSEDIR Like calling @code{AC_HEADER_DIRENT} and @code{AC_FUNC_CLOSEDIR_VOID}, but defines a different set of C preprocessor macros to indicate which header file is found. This macro and the names it defines are considered obsolete. The names it defines are: @c The printed table looks too spaced out with blank lines between the entries. @table @file @item dirent.h @code{DIRENT} @item sys/ndir.h @code{SYSNDIR} @item sys/dir.h @code{SYSDIR} @item ndir.h @code{NDIR} @end table In addition, if the @code{closedir} function does not return a meaningful value, define @code{VOID_CLOSEDIR}. @end defmac @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: @c The printed table looks too spaced out with blank lines between the entries. @table @file @item dirent.h @code{HAVE_DIRENT_H} @item sys/ndir.h @code{HAVE_SYS_NDIR_H} @item sys/dir.h @code{HAVE_SYS_DIR_H} @item ndir.h @code{HAVE_NDIR_H} @end table 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_STDC @maindex HEADER_STDC @cvindex STDC_HEADERS Define @code{STDC_HEADERS} if the system has 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 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 ANSI C requires. Use @code{STDC_HEADERS} instead of @code{__STDC__} to determine whether the system has ANSI-compliant header files (and probably C library functions) because many systems that have GCC do not have ANSI C header files. On systems without 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 ANSI and BSD; some are mostly ANSI but lack @samp{memmove}; some define the BSD functions as macros in @file{string.h} or @file{strings.h}; some have only the 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 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 # ifndef HAVE_STRCHR # define strchr index # define strrchr rindex # endif char *strchr (), *strrchr (); # ifndef 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 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_MEMORY_H @maindex MEMORY_H @cvindex NEED_MEMORY_H Define @code{NEED_MEMORY_H} if @code{memcpy}, @code{memcmp}, etc. are not declared in @file{string.h} and @file{memory.h} exists. This macro is obsolete; instead, use @code{AC_CHECK_HEADERS(memory.h)}. See the example for @code{AC_HEADER_STDC}. @end defmac @defmac AC_UNISTD_H @maindex UNISTD_H @cvindex HAVE_UNISTD_H Define @code{HAVE_UNISTD_H} if the system has @file{unistd.h}. This macro is obsolete; instead, use @samp{AC_CHECK_HEADERS(unistd.h)}. The way to check if the system supports 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 @cvindex _POSIX_VERSION @code{_POSIX_VERSION} is defined when @file{unistd.h} is included on POSIX.1 systems. If there is no @file{unistd.h}, it is definitely not a POSIX.1 system. However, some non-POSIX.1 systems do have @file{unistd.h}. @end defmac @defmac AC_USG @maindex USG @cvindex USG Define @code{USG} if the system does not have @file{strings.h}, @code{rindex}, @code{bzero}, etc. This implies that it has @file{string.h}, @code{strrchr}, @code{memset}, etc. The symbol @code{USG} is obsolete. Instead of this macro, see the example for @code{AC_HEADER_STDC}. @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}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]}) @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{} @r{[}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]]}) @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 caps). 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 Structures, Typedefs, Header Files, Existing Tests @section Structures The following macros check for certain structures or structure members. To check structures not listed here, you can use @code{AC_EGREP_CPP} (@pxref{Examining Declarations}) or @code{AC_TRY_LINK} (@pxref{Examining Libraries}) @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_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_STRUCT_ST_BLKSIZE @maindex STRUCT_ST_BLKSIZE @cvindex HAVE_ST_BLKSIZE If @code{struct stat} contains an @code{st_blksize} member, define @code{HAVE_ST_BLKSIZE}. @end defmac @defmac AC_STRUCT_ST_BLOCKS @maindex STRUCT_ST_BLOCKS @cvindex HAVE_ST_BLOCKS @ovindex LIBOBJS If @code{struct stat} contains an @code{st_blocks} member, define @code{HAVE_ST_BLOCKS}. Otherwise, add @samp{fileblocks.o} to the output variable @code{LIBOBJS}. @end defmac @defmac AC_STRUCT_ST_RDEV @maindex STRUCT_ST_RDEV @cvindex HAVE_ST_RDEV If @code{struct stat} contains an @code{st_rdev} member, define @code{HAVE_ST_RDEV}. @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_TM_ZONE}. Otherwise, if the external array @code{tzname} is found, define @code{HAVE_TZNAME}. @end defmac @node Typedefs, Compiler Characteristics, Structures, Existing Tests @section Typedefs The following macros check for C typedefs. If there is no macro specifically defined to check for a typedef you need, and you don't need to check for any special properties of it, then you can use a general typedef check macro. @menu * Particular Typedefs:: Special handling to find certain types. * Generic Typedefs:: How to find other types. @end menu @node Particular Typedefs, Generic Typedefs, , Typedefs @subsection Particular Typedef Checks These macros check for particular C typedefs. @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 If @code{mode_t} is not defined in @file{sys/types.h}, define @code{mode_t} to be @code{int}. @end defmac @defmac AC_TYPE_OFF_T @maindex TYPE_OFF_T @cvindex off_t If @code{off_t} is not defined in @file{sys/types.h}, define @code{off_t} to be @code{long}. @end defmac @defmac AC_TYPE_PID_T @maindex TYPE_PID_T @cvindex pid_t If @code{pid_t} is not defined in @file{sys/types.h}, define @code{pid_t} to be @code{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 If @code{size_t} is not defined in @file{sys/types.h}, define @code{size_t} to be @code{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 in @file{sys/types.h}, define @code{uid_t} to be @code{int} and @code{gid_t} to be @code{int}. @end defmac @node Generic Typedefs, , Particular Typedefs, Typedefs @subsection Generic Typedef Checks This macro is used to check for typedefs not covered by the particular test macros. @defmac AC_CHECK_TYPE (@var{type}, @var{default}) @maindex CHECK_TYPE If the type @var{type} is not defined in @file{sys/types.h}, define it to be the C (or C++) builtin type @var{default}; e.g., @samp{short} or @samp{unsigned}. @end defmac @node Compiler Characteristics, System Services, Typedefs, Existing Tests @section Compiler Characteristics The following macros check for C compiler or machine architecture features. You can use @code{AC_TRY_LINK} (@pxref{Examining Libraries}) or @code{AC_TRY_RUN} (@pxref{Run Time}) to check for characteristics not listed here. @defmac AC_C_BIGENDIAN @maindex C_BIGENDIAN @cvindex WORDS_BIGENDIAN 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 keyword @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. @end defmac @defmac AC_C_INLINE @maindex C_INLINE @cvindex inline If the C compiler is a version of GCC that supports the keyword @code{__inline} but not @code{inline} (such as some NeXT versions), define @code{inline} to be @code{__inline}. @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_CHECK_SIZEOF (@var{type}) @maindex CHECK_SIZEOF Define @code{SIZEOF_@var{uctype}} to be the size in bytes of the C (or C++) builtin type @var{type}, e.g. @samp{int} or @samp{char *}. If @samp{type} is unknown to the compiler, it gets a size of 0. @var{uctype} is @var{type}, with lowercase converted to uppercase, spaces changed to underscores, and asterisks changed to @samp{P}. 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 @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}. This macro is obsolete; it is more general to use @samp{AC_CHECK_SIZEOF(int)} instead. @end defmac @defmac AC_LONG_64_BITS @maindex LONG_64_BITS @cvindex LONG_64_BITS If the C type @code{long int} is 64 bits wide, define @code{LONG_64_BITS}. This macro is obsolete; it is more general to use @samp{AC_CHECK_SIZEOF(long)} instead. @end defmac @node System Services, UNIX Variants, Compiler Characteristics, Existing Tests @section System Services The following macros check for operating system services or capabilities. @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 variable @code{ac_cv_sys_interpreter}; it will be set to @samp{yes} if the system supports @samp{#!}, @samp{no} if not. @end defmac @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 @samp{--x-includes=@var{dir}} and @samp{--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 @samp{--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 An enhanced version of @code{AC_PATH_X}. Put the C compiler flags that X needs into output variable @code{X_CFLAGS}, and the X linker flags into @code{X_LIBS}. If X is not available, put @samp{-DX_DISPLAY_MISSING} into @code{X_CFLAGS}. Also check for special libraries that some systems need in order to compile X programs. Add any that the system needs to output variable @code{X_EXTRA_LIBS}. @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_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}. @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 BSD functions. Should be called before any macros that run the C compiler. @end defmac @defmac AC_DYNIX_SEQ @maindex DYNIX_SEQ If on Dynix/PTX (Sequent UNIX), add @samp{-lseq} to output variable @code{LIBS}. This macro is obsolete; instead, use @code{AC_FUNC_GETMNTENT}. @end defmac @defmac AC_IRIX_SUN @maindex IRIX_SUN If on IRIX (Silicon Graphics UNIX), add @samp{-lsun} to output variable @code{LIBS}. This macro is obsolete. 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)}. @end defmac @defmac AC_ISC_POSIX @maindex ISC_POSIX @cvindex _POSIX_SOURCE @ovindex CC If on a POSIXized ISC UNIX, define @code{_POSIX_SOURCE} and add @samp{-posix} (for the GNU C compiler) or @samp{-Xp} (for other C compilers) to output variable @code{CC}. This allows the use of 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 POSIX facilities. Should be called before any macros that run the C compiler. @end defmac @defmac AC_SCO_INTL @maindex SCO_INTL @ovindex LIBS If on SCO UNIX, add @samp{-lintl} to output variable @code{LIBS}. This macro is obsolete; instead, use @code{AC_FUNC_STRFTIME}. @end defmac @defmac AC_XENIX_DIR @maindex XENIX_DIR @ovindex LIBS If on Xenix, add @samp{-lx} to output variable @code{LIBS}. Also, if @file{dirent.h} is being used, add @samp{-ldir} to @code{LIBS}. This macro is obsolete; use @code{AC_HEADER_DIRENT} instead. @end defmac @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. @menu * Examining Declarations:: Detecting header files and declarations. * Examining Libraries:: Detecting functions and global variables. * Run Time:: Testing for run-time features. * Portable Shell:: Shell script portability pitfalls. * Testing Values and Files:: Checking strings and files. * Multiple Cases:: Tests for several possible values. * Language Choice:: Selecting which language to use for testing. @end menu @node Examining Declarations, Examining Libraries, , 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}, @var{action-if-true} @r{[}, @var{action-if-false}@r{]}) @maindex TRY_CPP @var{includes} is C or C++ @code{#include} statements and declarations, on which shell variable, backquote, 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 @samp{-g}, @samp{-O}, etc. are not valid options to many C preprocessors. @end defmac Here is now 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} @r{[}, @var{action-if-not-found}@r{]}) @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}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]}) @maindex EGREP_CPP @var{program} is the text of a C or C++ program, on which shell variable, backquote, 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 Libraries, Run Time, Examining Declarations, 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 Larry Wall's Metaconfig, which 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. The below macro is used to compile test programs to test for functions and global variables. It is also used to check for libraries, by adding the library being checked for to @code{LIBS} temporarily and trying to link a small program. And it is used to check matters of C syntax, such as whether a particular keyword is recognized---a test program using a keyword does not compile on systems that don't support it. @defmac AC_TRY_LINK (@var{includes}, @var{function-body}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]}) @maindex TRY_LINK Create a test C program to see whether a function whose body consists of @var{function-body} can be compiled and linked; @var{includes} is any @code{#include} statements needed by the code in @var{function-body}. If the file compiles and links successfully, run shell commands @var{action-if-found}, otherwise run @var{action-if-not-found}. This macro uses @code{CFLAGS} or @code{CXXFLAGS}, @code{CPPFLAGS}, @code{LDFLAGS}, and @code{LIBS} when compiling. @end defmac @defmac AC_COMPILE_CHECK (@var{echo-text}, @var{includes}, @var{function-body}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]}) @maindex COMPILE_CHECK This is an obsolete version of @code{AC_TRY_LINK}, with the addition that it prints @samp{checking for @var{echo-text}} to the standard output first, if @var{echo-text} is non-empty. @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 @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}, @var{action-if-true} @r{[}, @var{action-if-false} @r{[}, @var{action-if-cross-compiling}@r{]]}) @maindex TRY_RUN @var{program} is the text of a C program, on which shell variable and backquote 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 and this macro calls @code{AC_C_CROSS} if it has not already been called. 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 target 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_C_CROSS} 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. @defmac AC_C_CROSS @maindex C_CROSS If the C compiler being used does not produce executables that can run on the system where @code{configure} is being run, set the shell variable @code{cross_compiling} to @samp{yes}, otherwise @samp{no}. @end defmac @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 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, Testing Values and Files, 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 UNIX version 7, circa 1977. You should not use shell functions, aliases, 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! The set of external programs you should run in a @code{configure} script is fairly small. @xref{Utilities in Makefiles, , Utilities in Makefiles, standards.info, 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, as well; for example, don't rely on @code{ln} having a @samp{-f} option or @code{cat} having any options. 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. @node Testing Values and Files, Multiple Cases, Portable Shell, Writing Tests @section Testing Values and Files @code{configure} scripts need to test properties of many files and strings. Here are some portability problems to watch out for when doing those tests. 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 @code{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 @samp{-a} and @samp{-o}. On System V, the precedence of @samp{-a} and @samp{-o} is wrong relative to the unary operators; consequently, 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. To enable @code{configure} scripts to support cross-compilation, they shouldn't do anything that tests features of the host system instead of the target 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 4.3BSD does not have it. Another nonportable shell programming construction 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 BSD shells, including the Ultrix @code{sh}, don't accept the colon, and complain and die. A portable equivalent is @example : $@{@var{var}=@var{value}@} @end example @node Multiple Cases, Language Choice, Testing Values and Files, Writing Tests @section Multiple Cases Some operations are accomplished in several possible ways, depending on the 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 echo checking how to get filesystem type fstype=no # SVR4. AC_TRY_CPP([#include #include ], AC_DEFINE(FSTYPE_STATVFS) fstype=yes) if test $fstype = no; then # SVR3. AC_TRY_CPP([#include #include ], AC_DEFINE(FSTYPE_USG_STATFS) fstype=yes) fi if test $fstype = no; then # AIX. AC_TRY_CPP([#include #include ], AC_DEFINE(FSTYPE_AIX_STATFS) fstype=yes) fi @end group @end example @node Language Choice, , Multiple Cases, Writing Tests @section Language Choice 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_C @maindex LANG_C Do compilation tests using @code{CC} and @code{CPP} and use extension @file{.c} for test programs. @end defmac @defmac AC_LANG_CPLUSPLUS @maindex LANG_CPLUSPLUS Do compilation tests using @code{CXX} and @code{CXXCPP} and use extension @file{.C} for test programs. @end defmac @defmac AC_LANG_SAVE @maindex LANG_SAVE Remember the current language (as set by @code{AC_LANG_C} or @code{AC_LANG_CPLUSPLUS}) on a stack. Does not change which language is current. Use this macro and @code{AC_LANG_RESTORE} in macros that need to temporarily switch to a particular language. @end defmac @defmac AC_LANG_RESTORE @maindex LANG_RESTORE Select the language that is saved on the top of the stack, as set by @code{AC_LANG_SAVE}, and remove it from the stack. This macro is equivalent to either @code{AC_LANG_C} or @code{AC_LANG_CPLUSPLUS}, whichever had been run most recently when @code{AC_LANG_SAVE} was last called. Do not call this macro more times than @code{AC_LANG_SAVE}. @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 @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 users of progress or problems. @end menu @node Defining Symbols, Setting Output Variables, , 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. These two macros do that. @defmac AC_DEFINE (@var{variable} @r{[}, @var{value}@r{]}) @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_HEADER} 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 @code{m4} quote characters @samp{[} or @samp{]}), use @code{AC_DEFINE_UNQUOTED} instead. The following example defines the C preprocessor variable @code{EQUATION} to be the string constant @samp{"$a > $b"}: @example AC_DEFINE(EQUATION, "$a > $b") @end example @end defmac @defmac AC_DEFINE_UNQUOTED (@var{variable} @r{[}, @var{value}@r{]}) @maindex DEFINE_UNQUOTED Like @code{AC_DEFINE}, but three shell expansions are performed---once---on @var{variable} and @var{value}: variable expansion (@samp{$}), 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 By default, @code{AC_OUTPUT} substitutes the symbols defined by these macros into the output variable @code{DEFS}, which contains an option @samp{-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 "$ac_cv_func_vprintf" != yes; then AC_CHECK_FUNC(_doprnt, AC_DEFINE(HAVE_DOPRNT)) fi @end example If @code{AC_CONFIG_HEADER} has been called, then instead of substituting @code{DEFS}, @code{AC_OUTPUT} creates a header file by substituting the correct values into @code{#define} statements in a template file. @xref{Configuration Headers}, for more information about this kind of output. Due to the syntactical bizarreness of the Bourne shell, do not use semicolons to separate @code{AC_DEFINE} or @code{AC_DEFINE_UNQUOTED} calls from other macro calls or shell code; that can cause syntax errors in the resulting @code{configure} script. Use either spaces or newlines. That is, do this: @example AC_CHECK_HEADER(elf.h, AC_DEFINE(SVR4) LIBS="$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}) @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. The value of @var{variable} should not contain literal newlines. @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} substitute the contents of the file named by shell 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 the @file{Makefile.in} files with the contents of the file that the shell variable @var{variable} names when @code{AC_OUTPUT} is called. 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)dnl 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 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 @samp{--quiet} or @samp{--silent} option, print a message saying that the result was cached; otherwise, run the shell commands @var{commands-to-set-it}. Those commands should have no side effects except for setting the variable @var{cache-id}. In particular, they should not call @code{AC_DEFINE}; the code that follows the call to @code{AC_CACHE_VAL} should do that, based on the cached value. Also, they 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. 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. @end defmac @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 @subsection Cache Variable Names The names of cache variables should have the following format: @example @var{package-prefix}_cv_@var{value-type}_@var{specific-value}@r{[}_@var{additional-options}@r{]} @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. @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 Like their names, the values that may be assigned to cache variables have a few restrictions. The values may not contain single quotes or curly braces. 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 @file{./config.cache} as the cache file, creating it if it does not exist already. @code{configure} accepts the @samp{--cache-file=@var{file}} option to use a different cache file; that is what @code{configure} does when it calls @code{configure} scripts in subdirectories, so they share the cache. Giving @samp{--cache-file=/dev/null} disables caching, for debugging @code{configure}. @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 @samp{--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}). @node Printing Messages, , Caching Results, Results @section Printing Messages @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 backquote 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. @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 @samp{--quiet} or @samp{--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 @samp{--quiet} or @samp{--silent} option. @end defmac @defmac AC_MSG_ERROR (@var{error-description}) @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 stream and exits @code{configure} with a nonzero status. @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 stream; @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 The following two macros are an obsolete alternative to @code{AC_MSG_CHECKING} and @code{AC_MSG_RESULT}. @defmac AC_CHECKING (@var{feature-description}) @maindex CHECKING This macro is similar to @code{AC_MSG_CHECKING}, except that it prints a newline after the @var{feature-description}. It is useful mainly to print a general description of the overall purpose of a group of feature checks, e.g., @example AC_CHECKING(if stack overflow is detectable) @end example @end defmac @defmac AC_VERBOSE (@var{result-description}) @maindex VERBOSE This macro is similar to @code{AC_MSG_RESULT}, except that it is meant to follow a call to @code{AC_CHECKING} instead of @code{AC_MSG_CHECKING}; it starts the message it prints with a tab. It is considered obsolete. @end defmac @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. * Dependencies Between Macros:: What to do when macros depend on other macros. @end menu @node Macro Definitions, Macro Names, , Writing Macros @section Macro Definitions @maindex DEFUN Autoconf macros are defined using the @code{AC_DEFUN} macro, which is similar to the @code{m4} builtin @code{define} macro. In addition to defining a macro, @code{AC_DEFUN} adds to it some code which 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 @noindent The square brackets here do not indicate optional text: they should literally be present in the macro definition to avoid macro expansion problems (@pxref{Quoting}). You can refer to any arguments passed to the macro as @samp{$1}, @samp{$2}, etc. To introduce comments in @code{m4}, use the @code{m4} builtin @code{dnl}; it causes @code{m4} to discard the text through the next newline. It is not needed between macro definitions in @file{acsite.m4} and @file{aclocal.m4}, because all output is discarded until @code{AC_INIT} is called. @xref{Definitions, , How to define new macros, m4.info, GNU m4}, for more complete information on writing @code{m4} macros. @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 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 STRUCT Definitions of C structures in header files. @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. A macro that is an internal subroutine of another macro should have a name that starts with 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, Dependencies Between Macros, Macro Names, Writing Macros @section Quoting Macros that are called by other macros are evaluated by @code{m4} several times; each evaluation might require another layer of quotes to prevent unwanted expansions of macros or @code{m4} builtins, such as @samp{define} and @samp{$1}. Quotes are also required around macro arguments that contain commas, since commas separate the arguments from each other. It's a good idea to quote any macro arguments that contain newlines or calls to other macros, as well. Autoconf changes the @code{m4} quote characters from the default @samp{`} and @samp{'} to @samp{[} and @samp{]}, because many of the macros use @samp{`} and @samp{'}, mismatched. However, in a few places the macros need to use brackets (usually in C program text or regular expressions). In those places, they use the @code{m4} builtin command @code{changequote} to temporarily change the quote characters to @samp{<<} and @samp{>>}. (Sometimes, if they don't need to quote anything, they disable quoting entirely instead by setting the quote characters to empty strings.) Here is an example: @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 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 Dependencies Between Macros, , Quoting, 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. * Obsolete Macros:: Warning about old ways of doing things. @end menu @node Prerequisite Macros, Suggested Ordering, , 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 @code{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. @end defmac An alternative to using @code{AC_DEFUN} is to use @code{define} and call @code{AC_PROVIDE}. Because this technique does not prevent nested messages, it is considered obsolete. @defmac AC_PROVIDE (@var{this-macro-name}) @maindex PROVIDE Record the fact that @var{this-macro-name} has been called. @var{this-macro-name} should be the name of the macro that is calling @code{AC_PROVIDE}. An easy way to get it is from the @code{m4} builtin variable @code{$0}, like this: @example AC_PROVIDE([$0]) @end example @end defmac @node Suggested Ordering, Obsolete Macros, 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 @samp{-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 Obsolete Macros, , Suggested Ordering, Dependencies Between Macros @subsection Obsolete 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. Autoconf provides the @code{AC_OBSOLETE} macro to warn users producing @code{configure} scripts when they use obsolete macros, to encourage them to modernize. A sample call is: @example AC_OBSOLETE([$0], [; use AC_CHECK_HEADERS(unistd.h) instead])dnl @end example @defmac AC_OBSOLETE (@var{this-macro-name} @r{[}, @var{suggestion}@r{]}) @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}. @end defmac @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. It is possible to 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. * System Type Variables:: Variables containing the system type. * Using System Type:: What to do with the system type. @end menu @node Specifying Names, Canonicalizing, , Manual Configuration @section Specifying the System Type Like other 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: @example @var{cpu}-@var{company}-@var{system} @end example @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: @table @code @item --build=@var{build-type} the type of system on which the package is being configured and compiled (rarely needed); @item --host=@var{host-type} 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. @end table @noindent If the user gives @code{configure} a non-option argument, it is used as the default for the host, target, and build system types if the user does not specify them explicitly with options. The target and build types default to the host type if it is given and they are not. If you are cross-compiling, you still have to specify the names of the cross-tools you use, in particular the C compiler, on the @code{configure} command line, e.g., @example CC=m68k-coff-gcc configure --target=m68k-coff @end example @code{configure} recognizes short aliases for many system types; for example, @samp{decstation} can be given on the command line instead of @samp{mips-dec-ultrix4.2}. @code{configure} runs a script called @code{config.sub} to canonicalize system type aliases. @node Canonicalizing, System Type Variables, Specifying Names, Manual Configuration @section Getting the Canonical System Type The following macros make the system type available to @code{configure} scripts. They run the shell script @code{config.guess} to determine any values for the host, target, and build types that they need and the user did not specify on the command line. They run @code{config.sub} to canonicalize any aliases the user gave. If you use these macros, you must distribute those two shell scripts along with your source code. @xref{Output}, for information about the @code{AC_CONFIG_AUX_DIR} macro which you can use to control which directory @code{configure} looks for those scripts in. If you do not use either of these macros, @code{configure} ignores any @samp{--host}, @samp{--target}, and @samp{--build} options given to it. @defmac AC_CANONICAL_SYSTEM @maindex CANONICAL_SYSTEM Determine the system type and set output variables to the names of the canonical system types. @end defmac @defmac AC_CANONICAL_HOST @maindex CANONICAL_HOST Perform only the subset of @code{AC_CANONICAL_SYSTEM} relevant to the host type. This is all that is needed for programs that are not part of a compiler toolchain. @end defmac @node System Type Variables, Using System Type, Canonicalizing, Manual Configuration @section System Type Variables After calling @code{AC_CANONICAL_SYSTEM}, the following output variables contain the system type information. After @code{AC_CANONICAL_HOST}, only the @code{host} variables below are set. @table @code @ovindex build @ovindex host @ovindex target @item @code{build}, @code{host}, @code{target} the canonical system names; @item @code{build_alias}, @code{host_alias}, @code{target_alias} @ovindex build_alias @ovindex host_alias @ovindex target_alias the names the user specified, or the canonical names if @code{config.guess} was used; @item @code{build_cpu}, @code{build_vendor}, @code{build_os} @itemx @code{host_cpu}, @code{host_vendor}, @code{host_os} @itemx @code{target_cpu}, @code{target_vendor}, @code{target_os} @ovindex build_cpu @ovindex host_cpu @ovindex target_cpu @ovindex build_vendor @ovindex host_vendor @ovindex target_vendor @ovindex build_os @ovindex host_os @ovindex target_os the individual parts of the canonical names (for convenience). @end table @node Using System Type, , System Type Variables, 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 link those files, which have names based on the system name, to generic names, such as @file{host.h} or @file{target.c}. The @code{case} statement patterns can use shell wildcards 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 @defmac AC_LINK_FILES (@var{dest} @dots{}, @var{source} @dots{}) @maindex LINK_FILES 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. For example, this call: @example AC_LINK_FILES(config/sun3.h config/aout.h, host.h object.h) @end example @noindent creates in the current directory @file{host.h}, which is a link to @file{@var{srcdir}/config/sun3.h}, and @file{object.h}, which is a link to @file{@var{srcdir}/config/aout.h}. @end defmac @node Site Configuration, Invoking configure, 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. * 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 @section Working With External Software Some packages require, or can optionally use, other software packages which 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}@r{[}=@var{arg}@r{]} --without-@var{package} @end example For example, @samp{--with-gnu-ld} means work with the GNU linker instead of some other linker. @samp{--with-x11} means work with X11. 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}. @samp{--without-@var{package}} is equivalent to @samp{--with-@var{package}=no}. 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 what arguments are valid, is up to you. @defmac AC_ARG_WITH (@var{package}, @var{help-string}, @var{action-if-true} @r{[}, @var{action-if-false}@r{]}) @maindex ARG_WITH If the user gave @code{configure} the option @samp{--with-@var{package}} or @samp{--without-@var{package}}, run shell commands @var{action-if-true}. Otherwise run shell commands @var{action-if-false}. 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-true} in the shell variable @code{withval}. 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. @end defmac @defmac AC_WITH (@var{package}, @var{action-if-true} @r{[}, @var{action-if-false}@r{]}) @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, Site Details, 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}@r{[}=@var{arg}@r{]} --disable-@var{feature} @end example These options allow users to choose which optional features to build and install. @samp{--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 @samp{--enable-debug=stabs}. If no argument is given, it defaults to @samp{yes}. @samp{--disable-@var{feature}} is equivalent to @samp{--enable-@var{feature}=no}. 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 what arguments are valid, is up to you. @defmac AC_ARG_ENABLE (@var{feature}, @var{help-string}, @var{action-if-true} @r{[}, @var{action-if-false}@r{]}) @maindex ARG_ENABLE If the user gave @code{configure} the option @samp{--enable-@var{feature}} or @samp{--disable-@var{feature}}, run shell commands @var{action-if-true}. Otherwise run shell commands @var{action-if-false}. 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-true} in the shell variable @code{enableval}. The @var{help-string} argument is like that of @code{AC_ARG_WITH} (@pxref{External Software}). @end defmac @defmac AC_ENABLE (@var{feature}, @var{action-if-true} @r{[}, @var{action-if-false}@r{]}) @maindex ENABLE This is an obsolete version of @code{AC_ARG_ENABLE} that does not support providing a help string. @end defmac @node Site Details, Transforming Names, Package Options, 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. That approach is more convenient for users and makes the configuration process simpler than getting the information while configuring. @node Transforming Names, Site Defaults, Site Details, Site Configuration @section Transforming Program Names When Installing Autoconf supports giving @code{configure} command line options to change the names of programs being installed. 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 @samp{--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 also force a program name to begin with @file{g}, if you don't want GNU programs installed on your system to shadow system programs by the same name. For example, if GNU @code{make} used this mechanism, you could configure it with @samp{--program-prefix=g} and when you ran @samp{make install}, it would be installed as @file{/usr/local/bin/gmake}. The @code{configure} options are: @table @code @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. For example, you could use @example --program-transform-name='s/^/g/; s/^gg/g/; s/^gless/less/' @end example @noindent to prepend a @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 GNU programs. (That is assuming that you have a source tree containing those programs that is set up to use this option.) @end table In order to use the values given to these options, @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 above options are given to @code{configure}, program names are transformed accordingly. Otherwise, if @code{AC_CANONICAL_SYSTEM} has been called and a @samp{--target} value is given that differs from the host type (specified with @samp{--host} or defaulted by @code{config.sub}), the target type followed by a dash is used as a prefix. Otherwise, no program name transformation is done. @end defmac Here is how to use the variable @code{program_transform_name} in a @file{Makefile.in}: @example tn=@@program_transform_name@@ install: all $(INSTALL_PROGRAM) myprog $(bindir)/`echo myprog|sed '$(tn)'` @end example @noindent If you have more than one program to install, you can do it in a loop: @example PROGRAMS=cat ls rm install: for p in $(PROGRAMS); do \ $(INSTALL_PROGRAM) $$p $(bindir)/`echo $$p|sed '$(tn)'`; \ done @end example @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}/lib/config.site} if it exists, then @file{@var{exec_prefix}/lib/config.site} if it exists. Thus, settings in system-dependent files override those in system-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. 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{exec_prefix}/lib/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 configure scripts, or in the Autoconf @code{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/lib/config.site}. The command @samp{configure --prefix=/usr/share/local/gnu} would read this file (if @code{CONFIG_SITE} is not set). @example # config.site for configure # # Give Autoconf 2.x generated configure scripts a shared default # cache file for feature test results, architecture-specific. if test $cache_file = ./config.cache; then cache_file=/usr/local/gnu/lib/config.cache # A cache file is only valid for one C compiler. CC=gcc fi # Default --prefix and --exec-prefix. test $prefix = NONE && prefix=/usr/share/local/gnu test $exec_prefix = NONE && exec_prefix=/usr/local/gnu @end example @node Invoking configure, Invoking config.status, Site Configuration, Top @chapter Running @code{configure} Scripts 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. @menu * Basic Installation:: Instructions for typical cases. * Compilers and Options:: Selecting compilers and optimization. * Build Directory:: Configuring in a different directory. * Installation Names:: Installing in different directories. * System Type:: Specifying the system type. * Optional Features:: Selecting optional features. @end menu @include install.texi @node Invoking config.status, Concerns, Invoking configure, Top @chapter Recreating a Configuration The @code{configure} script creates a file named @file{config.status} which describes which configuration options were specified when the package was last configured. This file is a shell script which, if run, will recreate the same configuration. You can give @file{config.status} the @samp{--recheck} option to update itself. This option is useful if you change @code{configure}, so that the results of some tests might be different from the previous run. The @samp{--recheck} option re-runs @code{configure} with the same arguments you used before, plus the @samp{--no-create} option, which prevent @code{configure} from running @file{config.status} and creating @file{Makefile} and other files, and the @samp{--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). @file{config.status} also accepts the options @samp{--help}, which prints a summary of the options to @file{config.status}, and @samp{--version}, which prints the version of Autoconf used to create the @code{configure} script that generated @file{config.status}. @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 @samp{--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 The following variables 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 variables 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. @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} 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_HEADER}; if that macro was not called, @file{config.status} ignores this variable. @end defvar These variables also allow you to write @file{Makefile} rules that regenerate only some of the files. 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_FILES= CONFIG_HEADERS=config.h ./config.status echo > stamp-h Makefile: Makefile.in config.status CONFIG_FILES=Makefile CONFIG_HEADERS= ./config.status @end group @end example @noindent (If @file{configure.in} does not call @code{AC_CONFIG_HEADER}, there is no need to set @code{CONFIG_HEADERS} in the @code{make} rules.) @node Concerns, Upgrading, Invoking config.status, Top @chapter Concerns About Autoconf Several concerns about Autoconf come up occasionally. Here some of them are addressed. @menu * Copyright:: Legal restrictions on Autoconf output. * Why GNU m4:: Why not use the standard @code{m4}? * Bootstrapping:: Autoconf and GNU @code{m4} require each other? @end menu @node Copyright, Why GNU m4, , Concerns @section Copyright on @code{configure} Scripts @display What are the restrictions on distributing @code{configure} scripts that Autoconf generated? How does that affect my programs that use them? @end display The configuration scripts that Autoconf produces are covered by the GNU General Public License. This is because they consist almost entirely of parts of Autoconf itself, rearranged somewhat, and Autoconf is distributed under the terms of the GPL. As applied to Autoconf, the GPL just means that you need to distribute @file{configure.in}, and @file{acsite.m4}, @file{aclocal.m4}, @file{acconfig.h}, and @file{@var{config}.h.top} and @file{@var{config}.h.bot} if you use them, along with @code{configure}. Programs that use Autoconf scripts to configure themselves do not automatically come under the GPL. Distributing an Autoconf configuration script as part of a program is considered to be @emph{mere aggregation} of that work with the Autoconf script. Such programs are not derivative works based on Autoconf; only their configuration scripts are. 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. @node Why GNU m4, Bootstrapping, Copyright, Concerns @section Why Require GNU @code{m4}? @display Why does Autoconf require GNU @code{m4}? @end display Many @code{m4} implementations have hard-coded limitations on the size and number of macros, which 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 Since only software maintainers need to use Autoconf, and since GNU @code{m4} is simple to configure and install, it does not seem like an unreasonable burden to require GNU @code{m4} to be installed also. Most maintainers of GNU and other free software already have most of the GNU utilities installed, since they prefer them. @node Bootstrapping, , Why GNU m4, Concerns @section How Can I Bootstrap? @display If Autoconf requires GNU @code{m4} and GNU @code{m4} has an Autoconf @code{configure} script, how do I bootstrap? It seems like a chicken and egg problem! @end display Although GNU @code{m4} does come with a @code{configure} script produced by Autoconf, Autoconf is @emph{not} required in order to run the script and install GNU @code{m4}. Autoconf is only required if you want to @emph{change} the @code{m4} @code{configure} script, which few people have to do (mainly its maintainer). @node Upgrading, History, Concerns, Top @chapter 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. First, make sure you have GNU @code{m4} version 1.1 or higher installed, preferably 1.3 or higher. Versions before 1.1 have bugs that prevent them from working with Autoconf version 2. Versions 1.3 and later are much faster than earlier versions, because as of version 1.3, GNU @code{m4} has a more efficient implementation of diversions and can freeze its internal state in a file that it can read back quickly. @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. * Invoking autoupdate:: Replacing old macro names in @code{configure.in}. * 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, , Upgrading @section 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{Invoking autoconf}. If you distribute @file{install.sh} with your package, rename it to @file{install-sh} so @code{make} builtin rules won't inadvertantly 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{Invoking autoheader}. @node Changed Makefiles, Changed Macros, Changed File Names, Upgrading @section 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. 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 feature of replacing those variables without @samp{@@} characters around them has been removed. @node Changed Macros, Invoking autoupdate, Changed Makefiles, Upgrading @section 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{Old Macro Names}, 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{Invoking autoupdate}. 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}, 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 Invoking autoupdate, Changed Results, Changed Macros, Upgrading @section Using @code{autoupdate} to Modernize @code{configure} 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{Old Macro Names}, for a list of the old macro names 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 @code @item --help @itemx -h Print a summary of the command line options and exit. @item --macrodir=@var{dir} @itemx -m @var{dir} @evindex AC_MACRODIR Look for the Autoconf macro files in directory @var{dir} instead of the default installation directory. You can also set the @code{AC_MACRODIR} environment variable to a directory; this option overrides the environment variable. @item --version Print the version number of @code{autoupdate} and exit. @end table @node Changed Results, Changed Macro Writing, Invoking autoupdate, Upgrading @section 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 $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 backquotes) 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, Upgrading @section 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. @node History, Old Macro Names, Upgrading, 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 @code{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 @section Genesis In June 1991 I was maintaining many of the GNU utilities for the Free Software Foundation. As they were ported to more platforms and more programs were added, the number of @samp{-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 GNU utilities packages. Brian Berliner also adapted one of my scripts for his CVS revision control system. Later that summer, I learned that Richard Stallman and Richard Pixley were developing similar scripts to use in the 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 GNU utilities packages to use @code{configure} scripts, updating them all by hand became impractical. Rich Murphey, the maintainer of the 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 Larry Wall's Metaconfig program, 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); it was not being maintained at that time, and its scripts 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 @code{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 GNU extensions to @code{m4}.) Also, some of my friends at the University of Maryland had recently been putting @code{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 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 @code{m4} macros and continued to add features and improve the techniques used in the checks. Prominent among the testers were @ifinfo Franc,ois @end ifinfo @tex Fran\c cois @end tex Pinard, who came up with the idea of making an @file{autoconf} shell script to run @code{m4} and check for unresolved macro calls; Rich 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 Taylor, who added support for creating a C header file as an alternative to putting @samp{-D} options in a @file{Makefile}, so he could use Autoconf for his 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 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 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 @code{m4} implementations. UNIX @code{m4} started to dump core because of the length of the macros that Autoconf defined, and several bugs showed up in GNU @code{m4} as well. Eventually, we realized that we needed to use some features that only GNU @code{m4} has. 4.3BSD @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. @ifinfo Franc,ois @end ifinfo @tex Fran\c cois @end tex Pinard made it diagnose invalid arguments. Jim Blandy bravely coerced it into configuring GNU Emacs, laying the groundwork for several later improvements. Roland McGrath got it to configure the GNU C Library, wrote the @code{autoheader} script to automate the creation of C header file templates, and added a @samp{--verbose} option to @code{configure}. Noah Friedman added the @samp{--macrodir} option and @code{AC_MACRODIR} environment variable. 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}, @samp{--host}, and @samp{--target}; making links to files; and running @code{configure} scripts in subdirectories. Adding these features enabled Ken to convert 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 @ifinfo Franc,ois @end ifinfo @tex Fran\c cois @end tex Pinard, I made the macros not interrupt each others' messages. (That feature revealed some performance bottlenecks in GNU @code{m4}, which he hastily corrected!) I reorganized the documentation around problems people want to solve. And I began a testsuite, because experience had shown that Autoconf has a pronounced tendency to regress when we change it. Again, several alpha testers gave invaluable feedback, especially @ifinfo Franc,ois @end ifinfo @tex Fran\c cois @end tex Pinard, Jim Meyering, Karl Berry, Rob Savoye, and Ken Raeburn. Finally, version 2.0 was ready. And there was much rejoicing. (And I have free time again. I think.) @node Old Macro Names, Environment Variable Index, History, Top @chapter Old Macro Names In version 2 of Autoconf, most of the macros were renamed to use a more uniform and descriptive naming scheme. Here are the old names of the macros that were renamed, followed by the current names of those macros. Although the old names are still accepted by the @code{autoconf} program for backward compatibility, the old names are considered obsolete. @xref{Macro Names}, for a description of the new naming scheme. @table @code @item AC_ALLOCA @maindex ALLOCA @code{AC_FUNC_ALLOCA} @item AC_ARG_ARRAY @maindex ARG_ARRAY removed because of limited usefulness @item AC_CHAR_UNSIGNED @maindex CHAR_UNSIGNED @code{AC_C_CHAR_UNSIGNED} @item AC_CONST @maindex CONST @code{AC_C_CONST} @item AC_CROSS_CHECK @maindex CROSS_CHECK @code{AC_C_CROSS} @item AC_ERROR @maindex ERROR @code{AC_MSG_ERROR} @item AC_FIND_X @maindex FIND_X @code{AC_PATH_X} @item AC_FIND_XTRA @maindex FIND_XTRA @code{AC_PATH_XTRA} @item AC_FUNC_CHECK @maindex FUNC_CHECK @code{AC_CHECK_FUNC} @item AC_GCC_TRADITIONAL @maindex GCC_TRADITIONAL @code{AC_PROG_GCC_TRADITIONAL} @item AC_GETGROUPS_T @maindex GETGROUPS_T @code{AC_TYPE_GETGROUPS} @item AC_GETLOADAVG @maindex GETLOADAVG @code{AC_FUNC_GETLOADAVG} @item AC_HAVE_FUNCS @maindex HAVE_FUNCS @code{AC_CHECK_FUNCS} @item AC_HAVE_HEADERS @maindex HAVE_HEADERS @code{AC_CHECK_HEADERS} @item AC_HAVE_POUNDBANG @maindex HAVE_POUNDBANG @code{AC_SYS_INTERPRETER} (different calling convention) @item AC_HEADER_CHECK @maindex HEADER_CHECK @code{AC_CHECK_HEADER} @item AC_HEADER_EGREP @maindex HEADER_EGREP @code{AC_EGREP_HEADER} @item AC_INLINE @maindex INLINE @code{AC_C_INLINE} @item AC_LN_S @maindex LN_S @code{AC_PROG_LN_S} @item AC_LONG_DOUBLE @maindex LONG_DOUBLE @code{AC_C_LONG_DOUBLE} @item AC_LONG_FILE_NAMES @maindex LONG_FILE_NAMES @code{AC_SYS_LONG_FILE_NAMES} @item AC_MAJOR_HEADER @maindex MAJOR_HEADER @code{AC_HEADER_MAJOR} @item AC_MINUS_C_MINUS_O @maindex MINUS_C_MINUS_O @code{AC_PROG_CC_C_O} @item AC_MMAP @maindex MMAP @code{AC_FUNC_MMAP} @item AC_MODE_T @maindex MODE_T @code{AC_TYPE_MODE_T} @item AC_OFF_T @maindex OFF_T @code{AC_TYPE_OFF_T} @item AC_PID_T @maindex PID_T @code{AC_TYPE_PID_T} @item AC_PREFIX @maindex PREFIX @code{AC_PREFIX_PROGRAM} @item AC_PROGRAMS_CHECK @maindex PROGRAMS_CHECK @code{AC_CHECK_PROGS} @item AC_PROGRAMS_PATH @maindex PROGRAMS_PATH @code{AC_PATH_PROGS} @item AC_PROGRAM_CHECK @maindex PROGRAM_CHECK @code{AC_CHECK_PROG} @item AC_PROGRAM_EGREP @maindex PROGRAM_EGREP @code{AC_EGREP_CPP} @item AC_PROGRAM_PATH @maindex PROGRAM_PATH @code{AC_PATH_PROG} @item AC_REMOTE_TAPE @maindex REMOTE_TAPE removed because of limited usefulness @item AC_RESTARTABLE_SYSCALLS @maindex RESTARTABLE_SYSCALLS @code{AC_SYS_RESTARTABLE_SYSCALLS} @item AC_RETSIGTYPE @maindex RETSIGTYPE @code{AC_TYPE_SIGNAL} @item AC_RSH @maindex RSH removed because of limited usefulness @item AC_SETVBUF_REVERSED @maindex SETVBUF_REVERSED @code{AC_FUNC_SETVBUF_REVERSED} @item AC_SET_MAKE @maindex SET_MAKE @code{AC_PROG_MAKE_SET} @item AC_SIZEOF_TYPE @maindex SIZEOF_TYPE @code{AC_CHECK_SIZEOF} @item AC_SIZE_T @maindex SIZE_T @code{AC_TYPE_SIZE_T} @item AC_STAT_MACROS_BROKEN @maindex STAT_MACROS_BROKEN @code{AC_HEADER_STAT} @item AC_STDC_HEADERS @maindex STDC_HEADERS @code{AC_HEADER_STDC} @item AC_STRCOLL @maindex STRCOLL @code{AC_FUNC_STRCOLL} @item AC_ST_BLKSIZE @maindex ST_BLKSIZE @code{AC_STRUCT_ST_BLKSIZE} @item AC_ST_BLOCKS @maindex ST_BLOCKS @code{AC_STRUCT_ST_BLOCKS} @item AC_ST_RDEV @maindex ST_RDEV @code{AC_STRUCT_ST_RDEV} @item AC_SYS_SIGLIST_DECLARED @maindex SYS_SIGLIST_DECLARED @code{AC_DECL_SYS_SIGLIST} @item AC_TEST_CPP @maindex TEST_CPP @code{AC_TRY_CPP} @item AC_TEST_PROGRAM @maindex TEST_PROGRAM @code{AC_TRY_RUN} @item AC_TIMEZONE @maindex TIMEZONE @code{AC_STRUCT_TIMEZONE} @item AC_TIME_WITH_SYS_TIME @maindex TIME_WITH_SYS_TIME @code{AC_HEADER_TIME} @item AC_UID_T @maindex UID_T @code{AC_TYPE_UID_T} @item AC_UTIME_NULL @maindex UTIME_NULL @code{AC_FUNC_UTIME_NULL} @item AC_VFORK @maindex VFORK @code{AC_FUNC_VFORK} @item AC_VPRINTF @maindex VPRINTF @code{AC_FUNC_VPRINTF} @item AC_WAIT3 @maindex WAIT3 @code{AC_FUNC_WAIT3} @item AC_WARN @maindex WARN @code{AC_MSG_WARN} @item AC_WORDS_BIGENDIAN @maindex WORDS_BIGENDIAN @code{AC_C_BIGENDIAN} @item AC_YYTEXT_POINTER @maindex YYTEXT_POINTER @code{AC_DECL_YYTEXT} @end table @node Environment Variable Index, Output Variable Index, Old Macro Names, 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, , 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 @contents @bye @c Local variables: @c compile-command: "makeinfo autoconf.texi" @c End: