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Re: How to write directly to config.h from configure?

From: Nick Bowler
Subject: Re: How to write directly to config.h from configure?
Date: Thu, 26 Jul 2018 11:55:32 -0400

On 7/26/18, Jeffrey Walton <address@hidden> wrote:
> I have a bad interaction with a project and Autotools. The project is
> not an Autotools project but we are trying to [cleanly] support
> Autotools. The project provides its own config.h since the mid-1990's.
> We want to supply roughly the same file though Autotools.
> The problem is, the project's config.h has some stuff that does not
> seem to fit in the Autotools model like typedefs and declarations of
> namespaces. I think the solution is to write directly to config.h but
> I can't figure out how to do it. Testing code like below is lost
> (i.e., it is not in the resulting config.h):

The only thing configure (actually, config.status) does is replace
#undef lines in the package-provided with either a #define
or a comment, based on configure results controlled by the AC_DEFINE

You can essentially to place any code you'd like in, with
some limitations, see "Configuration Header Templates" in the Autoconf

> Is it possible to write directly to config.h? If yes, then how do I do it?

Configure just copies anything it doesn't recognize (i.e. anything other
than recognized #undef lines) from to config.h.

If you are generating using autoheader, then the AH_TOP and
AH_BOTTOM macros might be of interest.


Hope that helps,

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