Some macros should be run before another macro if both are called, but neither requires that the other be called. For example, a macro that changes the behavior of the C compiler should be called before any macros that run the C compiler. Many of these dependencies are noted in the documentation.
Autoconf provides the
AC_BEFORE macro to warn users when macros
with this kind of dependency appear out of order in a
configure.ac file. The warning occurs when creating
configure from configure.ac, not when running
AC_PROG_CPP checks whether the C compiler
can run the C preprocessor when given the -E option. It should
therefore be called after any macros that change which C compiler is
being used, such as
This warns the user if a call to
AC_PROG_CPP has already occurred
AC_PROG_CC is called.
Make M4 print a warning message to the standard error output if
called-macro-name has already been called. this-macro-name
should be the name of the macro that is calling
macro called-macro-name must have been defined using
AC_DEFUN or else contain a call to
AC_PROVIDE to indicate
that it has been called.