Checking default headers

[Ross Lagerwall]

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:
checking how to run the C preprocessor... gcc -E
checking for grep that handles long lines and -e... /usr/bin/grep
checking for egrep... /usr/bin/grep -E
checking for ANSI C header files... yes
checking for sys/types.h... yes
checking for sys/stat.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for memory.h... yes
checking for strings.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for unistd.h... yes
checking for unistd.h... (cached) yes

Is there a way of checking for the AC_INCLUDES_DEFAULT headers without
checking for anything else?
Calling _AC_INCLUDES_DEFAULT_REQUIREMENTS does this but it doesn't seem
to be a public macro.

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?

Lastly, AC_HEADER_STDC is declared obsolete yet it is required by
_AC_INCLUDES_DEFAULT_REQUIREMENTS.  Why is this?

Thanks
-- 
Ross Lagerwall