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(autoconf.info)Generic Functions

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Generic Function Checks
-----------------------

   These macros are used to find functions not covered by the
"particular" test macros.  If the functions might be in libraries other
than the default C library, first call `AC_CHECK_LIB' for those
libraries.  If you need to check the behavior of a function as well as
find out whether it is present, you have to write your own test for it
(Note: Writing Tests).

 - Macro: AC_CHECK_FUNC (FUNCTION, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND])
     If C function FUNCTION is available, run shell commands
     ACTION-IF-FOUND, otherwise ACTION-IF-NOT-FOUND.  If you just want
     to define a symbol if the function is available, consider using
     `AC_CHECK_FUNCS' instead.  This macro checks for functions with C
     linkage even when `AC_LANG(C++)' has been called, since C is more
     standardized than C++.  (Note: Language Choice, for more
     information about selecting the language for checks.)

 - Macro: AC_CHECK_FUNCS (FUNCTION..., [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND])
     For each FUNCTION in the whitespace-separated argument list,
     define `HAVE_FUNCTION' (in all capitals) if it is available.  If
     ACTION-IF-FOUND is given, it is additional shell code to execute
     when one of the functions is found.  You can give it a value of
     `break' to break out of the loop on the first match.  If
     ACTION-IF-NOT-FOUND is given, it is executed when one of the
     functions is not found.

   Autoconf follows a philosophy that was formed over the years by those
who have struggled for portability: isolate the portability issues in
specific files, and then program as if you were in a POSIX environment.
Some functions may be missing or unfixable, and your package must be
ready to replace them.

   Use the first three of the following macros to specify a function to
be replaced, and the last one (`AC_REPLACE_FUNCS') to check for and
replace the function if needed.

 - Macro: AC_LIBOBJ (FUNCTION)
     Specify that `FUNCTION.c' must be included in the executables to
     replace a missing or broken implementation of FUNCTION.

     Technically, it adds `FUNCTION.$ac_objext' to the output variable
     `LIBOBJS' and calls `AC_LIBSOURCE' for `FUNCTION.c'.  You should
     not directly change `LIBOBJS', since this is not traceable.

 - Macro: AC_LIBSOURCE (FILE)
     Specify that FILE might be needed to compile the project.  If you
     need to know what files might be needed by a `configure.ac', you
     should trace `AC_LIBSOURCE'.  FILE must be a literal.

     This macro is called automatically from `AC_LIBOBJ', but you must
     call it explicitly if you pass a shell variable to `AC_LIBOBJ'.  In
     that case, since shell variables cannot be traced statically, you
     must pass to `AC_LIBSOURCE' any possible files that the shell
     variable might cause `AC_LIBOBJ' to need.  For example, if you
     want to pass a variable `$foo_or_bar' to `AC_LIBOBJ' that holds
     either `"foo"' or `"bar"', you should do:

          AC_LIBSOURCE(foo.c)
          AC_LIBSOURCE(bar.c)
          AC_LIBOBJ($foo_or_bar)

     There is usually a way to avoid this, however, and you are
     encouraged to simply call `AC_LIBOBJ' with literal arguments.

     Note that this macro replaces the obsolete `AC_LIBOBJ_DECL', with
     slightly different semantics: the old macro took the function name,
     e.g. `foo', as its argument rather than the file name.

 - Macro: AC_LIBSOURCES (FILES)
     Like `AC_LIBSOURCE', but accepts one or more FILES in a
     comma-separated M4 list.  Thus, the above example might be
     rewritten:

          AC_LIBSOURCES([foo.c, bar.c])
          AC_LIBOBJ($foo_or_bar)

 - Macro: AC_REPLACE_FUNCS (FUNCTION...)
     Like `AC_CHECK_FUNCS', but uses `AC_LIBOBJ(FUNCTION)' as
     ACTION-IF-NOT-FOUND.  You can declare your replacement function by
     enclosing the prototype in `#if !HAVE_FUNCTION'.  If the system
     has the function, it probably declares it in a header file you
     should be including, so you shouldn't redeclare it lest your
     declaration conflict.