Re: Checking default headers

[Eric Blake]

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.

> 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?

> 
> 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

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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