Particular Function Checks

These macros check for particular C functions--whether they exist, and in some cases how they respond when given certain arguments.

Macro: AC_FUNC_ALLOCA

Check how to get alloca. Tries to get a builtin version by checking for `alloca.h' or the predefined C preprocessor macros __GNUC__ and _AIX. If this macro finds `alloca.h', it defines HAVE_ALLOCA_H.

If those attempts fail, it looks for the function in the standard C library. If any of those methods succeed, it defines HAVE_ALLOCA. Otherwise, it sets the output variable ALLOCA to `alloca.o' and defines C_ALLOCA (so programs can periodically call `alloca(0)' to garbage collect). This variable is separate from LIBOBJS so multiple programs can share the value of ALLOCA without needing to create an actual library, in case only some of them use the code in LIBOBJS.

This macro does not try to get alloca from the System V R3 `libPW' or the System V R4 `libucb' because those libraries contain some incompatible functions that cause trouble. Some versions do not even contain alloca or contain a buggy version. If you still want to use their alloca, use ar to extract `alloca.o' from them instead of compiling `alloca.c'.

Source files that use alloca should start with a piece of code like the following, to declare it properly. In some versions of AIX, the declaration of alloca must precede everything else except for comments and preprocessor directives. The #pragma directive is indented so that pre-ANSI C compilers will ignore it, rather than choke on it.

/* AIX requires this to be the first thing in the file.  */
#ifdef __GNUC__
# define alloca __builtin_alloca
#else
# if HAVE_ALLOCA_H
#  include <alloca.h>
# else
#  ifdef _AIX
 #pragma alloca
#  else
#   ifndef alloca /* predefined by HP cc +Olibcalls */
char *alloca ();
#   endif
#  endif
# endif
#endif

Macro: AC_FUNC_CLOSEDIR_VOID

If the closedir function does not return a meaningful value, define CLOSEDIR_VOID. Otherwise, callers ought to check its return value for an error indicator.

Macro: AC_FUNC_GETLOADAVG

Check how to get the system load averages. If the system has the getloadavg function, this macro defines HAVE_GETLOADAVG, and adds to LIBS any libraries needed to get that function.

Otherwise, it adds `getloadavg.o' to the output variable LIBOBJS, and possibly defines several other C preprocessor macros and output variables:

1. It defines SVR4, DGUX, UMAX, or UMAX4_3 if on those systems.
2. If it finds `nlist.h', it defines NLIST_STRUCT.
3. If `struct nlist' has an `n_un' member, it defines NLIST_NAME_UNION.
4. If compiling `getloadavg.c' defines LDAV_PRIVILEGED, programs need to be installed specially on this system for getloadavg to work, and this macro defines GETLOADAVG_PRIVILEGED.
5. This macro sets the output variable NEED_SETGID. The value is `true' if special installation is required, `false' if not. If NEED_SETGID is `true', this macro sets KMEM_GROUP to the name of the group that should own the installed program.

Macro: AC_FUNC_GETMNTENT

Check for getmntent in the `sun', `seq', and `gen' libraries, for Irix 4, PTX, and Unixware, respectively. Then, if getmntent is available, define HAVE_GETMNTENT.

Macro: AC_FUNC_GETPGRP

If getpgrp takes no argument (the POSIX.1 version), define GETPGRP_VOID. Otherwise, it is the BSD version, which takes a process ID as an argument. This macro does not check whether getpgrp exists at all; if you need to work in that situation, first call AC_CHECK_FUNC for getpgrp.

Macro: AC_FUNC_MEMCMP

If the memcmp function is not available, or does not work on 8-bit data (like the one on SunOS 4.1.3), add `memcmp.o' to output variable LIBOBJS.

Macro: AC_FUNC_MMAP

If the mmap function exists and works correctly on memory mapped files, define HAVE_MMAP.

Macro: AC_FUNC_SETVBUF_REVERSED

If setvbuf takes the buffering type as its second argument and the buffer pointer as the third, instead of the other way around, define SETVBUF_REVERSED. This is the case on System V before release 3.

Macro: AC_FUNC_STRCOLL

If the strcoll function exists and works correctly, define HAVE_STRCOLL. This does a bit more than `AC_CHECK_FUNCS(strcoll)', because some systems have incorrect definitions of strcoll, which should not be used.

Macro: AC_FUNC_STRFTIME

Check for strftime in the `intl' library, for SCO UNIX. Then, if strftime is available, define HAVE_STRFTIME.

Macro: AC_FUNC_UTIME_NULL

If `utime(file, NULL)' sets file's timestamp to the present, define HAVE_UTIME_NULL.

Macro: AC_FUNC_VFORK

If `vfork.h' is found, define HAVE_VFORK_H. If a working vfork is not found, define vfork to be fork. This macro checks for several known errors in implementations of vfork and considers the system to not have a working vfork if it detects any of them. It is not considered to be an implementation error if a child's invocation of signal modifies the parent's signal handler, since child processes rarely change their signal handlers.

Macro: AC_FUNC_VPRINTF

If vprintf is found, define HAVE_VPRINTF. Otherwise, if _doprnt is found, define HAVE_DOPRNT. (If vprintf is available, you may assume that vfprintf and vsprintf are also available.)

Macro: AC_FUNC_WAIT3

If wait3 is found and fills in the contents of its third argument (a `struct rusage *'), which HP-UX does not do, define HAVE_WAIT3.