Re: PACKAGE_FOO macros

[Guido Draheim]

> The most usual thing you want to do is to include or not include various
> headers depending on whether they are present or not.  One way of doing this
> is to write .h.in into which config.status can substitute #include
> directives.  The current macro I have for this is shown below - it's not
> wonderful, but it gets the job done for me.  This is the sort of macro you
> need once you have determined that you need the header file, it is not a
> feature test macro.

Exactly that's the case why I wrote prefix_config_h - so that I do *not*
have to maintain a dozen .h.in files with their shell-code in configure
plus making the two interdependent plus being dependent on autotools.

The prefixed config header *can* be installed - along with the normal
package headers where there are some #ifdefs which carry the logic
that is otherwise in a configure - to conditionally include system
headers from within package headers. Furthermore, one can place some
ac_defines that tell about some config options that one can #ifdef
other parts in the headers, e.g. some typedefs.

Furthermore, such an #ifdef scheme is independent of autotools - some
project just detects MSVC and includes msvc-config.h that carries
those prefixed defines that match the compile environment of that
compiler. No configure-run is needed beforehand - but if another system
can run ./configure then it will more closely be able to autconfigure
the package to the environment present at that time.

The thing that currently bothers me: the prefix_config_h is not folded
with todays config_header functionality. It does not even add its
mechanics to config.status which it should - the prefix_header is only
remade at the next ./configure. No immediate reconf here.

Furthermore, one could think to fully fold it with todays config_header,
e.g. let there be an alternative AC_PREFIX_CONFIG_HEADER to be in the
place of config_header - all the other modes would still work as with
creating a normal config.h but this time it is a prefixed one. I'm
sure that'd make a lot of people happy...

-- cheers, guido                       example: http://zziplib.sf.net