Re: Checking default headers

[Ross Lagerwall]

On Tue, Sep 03, 2013 at 08:52:54AM -0600, Eric Blake wrote:
> On 09/02/2013 08:03 AM, Ross Lagerwall wrote:
> > Hi,
> > 
> > I have a question about checking headers.
> > 
> > Suppose I have a simple program which includes unistd.h and nothing
> > else.  I could AC_CHECK_HEADERS([unistd.h]) but then it checks for the
> > header twice because using AC_CHECK_HEADERS implies checking a whole
> > bunch of headers:
> 
> > 
> > Is there a way of checking for the AC_INCLUDES_DEFAULT headers without
> > checking for anything else?
> 
> Not particularly, but there IS a way to avoid AC_INCLUDES_DEFAULT in the
> first place:
> 
> AC_CHECK_HEADERS([unistd.h], , , [ ])
> 
> to force a non-empty fourth argument to bypass the default use of
> AC_INCLUDES_DEFAULT.

OK, thanks.

> 
> > Secondly, AC_TYPE_UINT32_T gives different results depending on whether
> > any headers have been checked before (eg. if I first check for dlfcn.h,
> > stdint.h is automatically checked for, but otherwise it is not).
> > This seems nonintuitive; is it supposed to be like this?
> 
> Probably means that AC_TYPE_UINT32_T is missing a prereq on the standard
> headers; would you mind posting a reproducible test case, and we can
> work on fixing the bug?

The following reproduces it:
"""
AC_INIT([test], [dev])
AC_PROG_CC

if false; then
    AC_CHECK_HEADERS([pthread.h], [], [have_pthreads=no])
fi

AC_TYPE_UINT16_T
AC_OUTPUT
"""

There seems to be some interaction with AC_CHECK_HEADERS being performed
conditionally.

> 
> > 
> > Lastly, AC_HEADER_STDC is declared obsolete yet it is required by
> > _AC_INCLUDES_DEFAULT_REQUIREMENTS.  Why is this?
> 
> Commit f52459d has already tried to address that, and is just awaiting
> the release of autoconf 2.70.  Is there anything further we need to fix?
> 
> git.sv.gnu.org/gitweb/?p=autoconf.git;a=commitdiff;h=f52459d
> 

Well the following removes the "checking for ANSI C header files... yes"
line which seems to appear when AC_HEADER_STDC is called.

Regards
Ross Lagerwall

8<------------------------------
>From 5ef0afde59e1c3561df4462cfaa974706ffb8b76 Mon Sep 17 00:00:00 2001
From: Ross Lagerwall <address@hidden>
Date: Tue, 3 Sep 2013 19:40:09 +0200
Subject: [PATCH] Remove call to the obsolete AC_HEADER_STDC

---
 lib/autoconf/headers.m4 | 1 -
 1 file changed, 1 deletion(-)

diff --git a/lib/autoconf/headers.m4 b/lib/autoconf/headers.m4
index 7f5dbce..cc7e1c8 100644
--- a/lib/autoconf/headers.m4
+++ b/lib/autoconf/headers.m4
@@ -329,7 +329,6 @@ ac_includes_default="\
 # include <unistd.h>
 #endif"
 ])dnl
-AC_REQUIRE([AC_HEADER_STDC])dnl
 # On IRIX 5.3, sys/types and inttypes.h are conflicting.
 AC_CHECK_HEADERS([sys/types.h sys/stat.h stdlib.h string.h memory.h strings.h \
                  inttypes.h stdint.h unistd.h],
-- 
1.8.4