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How to undefine a macro in configure.ac

I am writing my configure.ac script, and have a few custom enable arguments which define macros in my C code if enabled. An example:

AC_ARG_ENABLE([example],
    AS_HELP_STRING([--enable-example], [This is an example]))
AS_IF([test "x$enable_example" = "xyes"], [
      AC_DEFINE(EXAMPLE_MACRO, 1, [This is a definition example])
      ])

Now say I have an enable option which, if enabled, must disable the effects of --enable-example option. I have the normal setup:

AC_ARG_ENABLE([another-feature],
    AS_HELP_STRING([--another-feature], [This is a feature which enables something, but disables --enable-example]))
AS_IF([test "x$enable_another_feature" = "xyes"], [
      AC_DEFINE(ANOTHER_FEATURE_MACRO, 1, [This is another feature definition])
      ])

Now I need to be able to undefine the EXAMPLE_MACRO macro, but I can't find anything to undo the AC_DEFINE. Am I missing something?

Solution

  • Why not simply delay the AC_DEFINE function calls? Note, I'm not a big fan of the AS_IF macro...

    if test "x$enable_another_feature" = xyes ; then
  # enable_example="no" # (optional)
  AC_DEFINE([ANOTHER_FEATURE_MACRO], [1])
elif test "x$enable_example" = xyes ; then
  AC_DEFINE([EXAMPLE_MACRO], [1])
fi

    If the AC_DEFINE is not executed, the corresponding #define ... is not instantiated in the config header. Discussed here.