ac-archive: ax_prefix_config_h.m4 - newest variant..

[Guido Draheim]

The newest variant for making prefixed config.h defines is now up at
the sfnet ac-archive - I did just found a last bug, and after having
it used in a few projects of mine, I think it is now time to make
them available to the world ;-) ... all the other prefix_config_h
macros are now marked "obsolete".

The AX_PREFIX_CONFIG_H macro does now properly nest itself into the
usual autoconf scheme by adding the actual functionality to the
config.status script, and it does also get its input-header from
the var-name used by AM_CONFIG_HEADER. In most places, it should
be sufficient now to mention AX_PREFIX_CONFIG_H anywhere in your
configure.ac script :-)

http://ac-archive.sf.net/guidod/ax_prefix_config_h.html

Description (a copy from above's html link...)

this is a new variant from ac_prefix_config_    this one will use a
lowercase-prefix if  the config-define was starting with a lowercase-char,
e.g.
   #define const or #define restrict or #define off_t
   (and this one can live in another directory, e.g. testpkg/config.h
    therefore I decided to move the output-header to be the first arg)

takes the usual config.h generated header file; looks for each of the
generated "#define SOMEDEF" lines, and prefixes the defined name (ie.
makes it "#define PREFIX_SOMEDEF". The result is written to the output
config.header file. The PREFIX is converted to uppercase for the conversions.

default OUTPUT-HEADER = $PACKAGE-config.h
default PREFIX = $PACKAGE
default ORIG-HEADER, from AM_CONFIG_HEADER(config.h)

Your configure.ac script should contain both macros in this order, and
unlike the earlier variations of this prefix-macro it is okay to place
the AX_PREFIX_CONFIG_H call before the AC_OUTPUT invokation.

example:    AC_INIT(config.h.in)        # config.h.in as created by "autoheader"
   AM_INIT_AUTOMAKE(testpkg, 0.1.1)    # makes #undef VERSION and PACKAGE
   AM_CONFIG_HEADER(config.h)          # prep config.h from config.h.in
   AX_PREFIX_CONFIG_H(mylib/_config.h) # prep mylib/_config.h from it..
   AC_MEMORY_H                         # makes "#undef NEED_MEMORY_H"
   AC_C_CONST_H                        # makes "#undef const"
   AC_OUTPUT(Makefile)                 # creates the "config.h" now
                                       # and also mylib/_config.h

if the argument to AX_PREFIX_CONFIG_H would have been omitted then the
default outputfile would have been called simply "testpkg-config.h", but
even under the name "mylib/_config.h" it contains prefix-defines like
   #ifndef TESTPKG_VERSION
   #define TESTPKG_VERSION "0.1.1"
   #endif
   #ifndef TESTPKG_NEED_MEMORY_H
   #define TESTPKG_NEED_MEMORY_H 1
   #endif
   #ifndef _testpkg_const
   #define _testpkg_const _const
   #endif

   and this "mylib/_config.h" can be installed along with other
   header-files, which is most convenient when creating a shared
   library (that has some headers) where some functionality is
   dependent on the OS-features detected at compile-time. No
   need to invent some "mylib-confdefs.h.in" manually. :-)

Note that some AC_DEFINEs that end up in the config.h file are actually
self-referential - e.g. AC_C_INLINE, AC_C_CONST, and the AC_TYPE_OFF_T
say that they "will define inline|const|off_t if the system does not
do it by itself". You might want to clean up about these - consider
an extra mylib/conf.h that reads something like:

    #include <mylib/_config.h>
    #ifndef _testpkg_const
    #define _testpkg_const const
    #endif

and then start using _testpkg_const in the header files. That is also
a good thing to differentiate whether some library-user has starting
to take up with a different compiler, so perhaps it could read something
like this:

   #ifdef _MSC_VER
   #include <mylib/_msvc.h>
   #else
   #include <mylib/_config.h>
   #endif
   #ifndef _testpkg_const
   #define _testpkg_const const
   #endif