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No longer use CPP to check for the existing of headers: use CC to

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check for compilability.
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Paul Eggert 2002-10-11 23:53:09 +00:00
parent 7006b6880c
commit cc332d2334
3 changed files with 20 additions and 34 deletions
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8
ChangeLog
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@ -1,5 +1,13 @@
2002-10-11 Akim Demaille <akim@epita.fr>
No longer use CPP to check for the existing of headers: use CC to
check for compilability.
* lib/autoconf/headers.m4 (_AC_CHECK_HEADER_MONGREL)
(AC_CHECK_HEADER, _AC_CHECK_HEADER_OLD): Remove.
(_AC_CHECK_HEADER_NEW): Rename as...
(AC_CHECK_HEADER): this.
* lib/autotest/general.m4 (AT_INIT): Include the failed test
numbers in the Subject suggestion.

4
NEWS
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@ -3,6 +3,10 @@
** Macros
- AC_CHECK_HEADER/AC_CHECK_HEADERS
These macros now check whether the headers are compilable, i.e., they
compile headers rather than merely preprocess them.
- New macros
AC_FUNC_MBRTOWC

42
doc/autoconf.texi
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@ -4459,42 +4459,19 @@ test for it (@pxref{Writing Tests}).
@defmac AC_CHECK_HEADER (@var{header-file}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes})
@acindex CHECK_HEADER
If the system header file @var{header-file} is usable, execute shell
If the system header file @var{header-file} is compilable, 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.
The meaning of ``usable'' depends upon the content of @var{includes}:
@table @asis
@item if @var{includes} is empty
check whether
@example
@var{header-file}
@end example
@noindent
can be @emph{preprocessed} without error.
@item if @var{include} is set
Check whether
@example
@var{includes}
#include <@var{header-file}>
@end example
@noindent
can be @emph{compiled} without error. You may use
@code{AC_CHECK_HEADER} (and @code{AC_CHECK_HEADERS}) to check whether
two headers are compatible.
@end table
You may pass any kind of dummy content for @var{includes}, such as a
single space or a comment, to check whether @var{header-file} compiles
with success.
Previous versions of Autoconf merely checked whether the header was
accepted by the preprocessor. This was changed because the old test
was inappropriate for typical uses. Headers are typically used to
compile, not merely to preprocess, and the old behavior sometimes
accepted headers that clashed at compile-time. If you need to check
whether a header is preprocessable, you can use @code{AC_TRY_CPP} or
one of its variants (@pxref{Examining Declarations}).
@end defmac
@defmac AC_CHECK_HEADERS (@var{header-file}@dots{}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes})
@ -4507,9 +4484,6 @@ 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.
Be sure to read the documentation of @code{AC_CHECK_HEADER} to
understand the influence of @var{includes}.
@end defmac
@node Declarations