[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

9.1 Macro Definitions

Autoconf macros are defined using the AC_DEFUN macro, which is similar to the M4 builtin define macro. In addition to defining a macro, AC_DEFUN adds to it some code that is used to constrain the order in which macros are called (see section 9.4.1 Prerequisite Macros).

An Autoconf macro definition looks like this:

 
AC_DEFUN(macro-name, macro-body)

You can refer to any arguments passed to the macro as `$1', `$2', etc. See section `How to define new macros' in GNU m4, for more complete information on writing M4 macros.

Be sure to properly quote both the macro-body and the macro-name to avoid any problems if the macro happens to have been previously defined.

Each macro should have a header comment that gives its prototype, and a brief description. When arguments have default values, display them in the prototype. For example:

 
# AC_MSG_ERROR(ERROR, [EXIT-STATUS = 1])
# --------------------------------------
define([AC_MSG_ERROR],
[{ _AC_ECHO([configure: error: $1], 2); exit m4_default([$2], 1); }])

Comments about the macro should be left in the header comment. Most other comments will make their way into `configure', so just keep using `#' to introduce comments.

If you have some very special comments about pure M4 code, comments that make no sense in `configure' and in the header comment, then use the builtin dnl: it causes m4 to discard the text through the next newline.

Keep in mind that dnl is rarely needed to introduce comments; dnl is more useful to get rid of the newlines following macros that produce no output, such as AC_REQUIRE.



This document was generated by Davide on March, 6 2002 using texi2html