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Re: CXXLINK in generated Makefiles

From: Dale E. Martin
Subject: Re: CXXLINK in generated Makefiles
Date: Mon, 6 Dec 2004 10:08:14 -0500
User-agent: Mutt/1.5.4i

On Sun, Dec 05, 2004 at 06:55:23AM +0100, Alexandre Duret-Lutz wrote:
>  Dale> AC_SUBST(CXX)
> This is superfluous if you already call AC_PROG_CXX.

OK, I've wondered about that.
> This will override the Automake definition of this variable with
> the configure definition of it (which is empty, unless you set
> the variable explicitly).

I see.
>  Dale> Any package including C++ code must define the output variable `CXX' in
>  Dale> `'; the simplest way to do this is to use the `AC_PROG_CXX'
>  Dale> macro (*note Particular Program Checks: (autoconf)Particular 
> Programs.).
> This means that CXX is not defined by Automake.

OK, after digesting this email thread I can see how it could mean that.

>  Dale> A few additional variables are defined when a C++ source file is
>  Dale> seen:
>  Dale> [snip]
>  Dale> `CXXLINK'
>  Dale> The command used to actually link a C++ program.
> This means that CXXLINK is defined by Automake in Makefiles with
> C++ source files.  It does not means that CXXLINK is defined at
> configure time.  Automake just defines the variable in the
> Makefile.ins it outputs.

Perhaps that part of the documentation could be more explicit.  "Automake
does not define CXX - that must be defined externally.  To have autoconf
define it, many applications use AC_PROG_CXX.  The following are defined by
automake in generated Makefiles" or something like that.
> I can't think of any clean way to obtain the Automake definition of
> CXXLINK for a non-Automake Makefile.  (One idea would be to generate your
> by extracting the interesting bits of an
> automake-generated

I'll mull that one over.

> I believe the simplest solution is to call libtool as you always did, and
> simply add the missing --tag=CXX option.

The problem with that is that libtool < 1.5 does not support that option
and dies an ugly death when it's present.  I guess I need to figure out how
to write an autoconf test to figure out the libtool version.  Any
suggestions welcome - I'm certainly no autoconf wizard!

Dale E. Martin, Clifton Labs, Inc.
Senior Computer Engineer
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