| I finally got around to do some testing with real-world software.
| So far, I haven't seen any major problems, but there are a few
| little things I'd like to have explained, as I didn't follow the
| discussions here too closely.
|
| Consider the following configure.in fragment. It checks whether the
| sig_atomic_t type is defined in signal.h, and whether it's declared
| volatile:
|
| AC_MSG_CHECKING(for sig_atomic_t in signal.h)
| AC_EGREP_HEADER(sig_atomic_t,signal.h,
| [
| ac_cv_type_sig_atomic_t=yes;
| AC_EGREP_HEADER(volatile.*sig_atomic_t,
| signal.h,
| [
| is_sig_atomic_t_volatile=yes;
| AC_MSG_RESULT([yes, volatile])
| ],
| [
| is_sig_atomic_t_volatile=no;
| AC_MSG_RESULT([yes, non volatile])
| ])
| ],
| [
| AC_MSG_RESULT(no)
| AC_CHECK_TYPE(sig_atomic_t, int)
| is_sig_atomic_t_volatile=no
| ])
|
| An autoconf 2.13 generated configure script generates the following output:
|
| checking for sig_atomic_t in signal.h... yes, non volatile
|
| An autoconf 2.49e (today's cvs) creates this output:
|
| checking for sig_atomic_t in signal.h... checking for stdlib.h... yes
| checking for string.h... (cached) yes
| checking for memory.h... yes
| checking for strings.h... yes
| checking for inttypes.h... yes
| checking for unistd.h... yes
| yes, non volatile
|
| I'd like to know why autoconf inserts this "virtual" AC_CHECK_HEADERS
| code.
Generic Type Checks
-------------------
These macros are used to check for types not covered by the
"particular" test macros.
- Macro: AC_CHECK_TYPE (TYPE, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND], [INCLUDES])
Check whether TYPE is defined. It may be a compiler builtin type
or defined by the [INCLUDES] (*note Default Includes::).
and
Default Includes
----------------
Several tests depend upon a set of header files. Since these headers
are not universally available, tests actually have to provide a set of
protected includes, such as:
#if TIME_WITH_SYS_TIME
# include <sys/time.h>
# include <time.h>
#else
# if HAVE_SYS_TIME_H
# include <sys/time.h>
# else
# include <time.h>
# endif
#endif
Unless you know exactly what you are doing, you should avoid using
unconditional includes, and check the existence of the headers you
include beforehand (*note Header Files::).
Most generic macros provide the following default set of includes:
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#if STDC_HEADERS
# include <stdlib.h>
# include <stddef.h>
#else
# if HAVE_STDLIB_H
# include <stdlib.h>
# endif
#endif
#if HAVE_STRING_H
# if !STDC_HEADERS && HAVE_MEMORY_H
# include <memory.h>
# endif
# include <string.h>
#else
# if HAVE_STRINGS_H
# include <strings.h>
# endif
#endif
#if HAVE_INTTYPES_H
# include <inttypes.h>
#endif
#if HAVE_UNISTD_H
# include <unistd.h>
#endif
If the default includes are used, then Autoconf will automatically
check for the presence of these headers, i.e., you don't need to run
`AC_HEADERS_STDC', nor check for `stdlib.h' etc.
