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

check for compilability.

diff --git a/ChangeLog b/ChangeLog
index 856d8bf8204c1c7609a5d4f4d56f55d60049b554..9e4390ce71eb54ecc0dabe6939a3daf5201811cd 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -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.
 

diff --git a/NEWS b/NEWS
index e0bef5a3865d7468c406b39b8eae4110759ecf6e..e197bf5e318ce6bf57cffaff404ffe56ae7010d3 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -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
 

diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 141455d28508b40869b6650903e02fbfb183ba1e..a57c41f10cb71689de96bde2c3de2b304d020b23 100644 (file)
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -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