Next: Macro Names, Up: Writing Autoconf Macros
Autoconf macros are defined using the AC_DEFUN
macro, which is
similar to the M4 builtin m4_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 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 How to define new macros, 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]) # -------------------------------------- m4_define([AC_MSG_ERROR], [{ AS_MESSAGE([error: $1], [2]) exit m4_default([$2], [1]); }])
Comments about the macro should be left in the header comment. Most other comments make their way into configure, so just keep using `#' to introduce comments.
If you have some 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
.