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Re: autoconf 2.61: AC_DEFINE variable with parenthesis

From: Paul Eggert
Subject: Re: autoconf 2.61: AC_DEFINE variable with parenthesis
Date: Wed, 27 Dec 2006 13:21:35 -0800
User-agent: Gnus/5.1008 (Gnus v5.10.8) Emacs/21.4 (gnu/linux)

"Steven G. Johnson" <address@hidden> writes:

> Paul Eggert wrote:
>> That could well be, but it was never documented and it's not clear
>> to me what the semantics would be.  Are arbitrary characters allowed
>> in the macro name?  Surely not.
> No, just things that are valid in cpp #defines.

Surely that's too strong as well.  Are ellipses "..." allowed?  How
about C comments, Universal Character Names and UTF-8 in names?  Or
backslash-newline, which can occur between any two pairs of characters
in the above?  Or trigraphs lke "??=" and "??/"?  These are all valid
in cpp #defines, before the ")" that closes the argument list.

This stuff can get hairy pretty quickly, which is why we'd need to
document exactly what we support, if we want to support it.

>> What happens if we have
>> AC_DEFINE([NAME(x)], ...) followed by AC_DEFINE([NAME(y)], ...)
>> followed by AC_DEFINE([NAME], ...)?
> The same thing that happens if you do AC_DEFINE([NAME],[VAL1])
> followed by AC_DEFINE([NAME],[VAL2]): the last definition encountered
> is the one used.

That actually worked, despite the change in spelling among [NAME(x)]
and [NAME(y)] and [NAME]?  That's news to me.  But again, whatever the
rule is, it should be documented.  For example, what would happen if
there's white space in the name, e.g., [NAME(x, y)] or [ NAME] or
[NAME ]?

> I think you're making it out to be more complicated than it is.

Maybe.  Perhaps it's because I've been burned by cpp too many

> In the @defmac AC_DEFINE, in autoconf.tex, all we need to do is to
> add a single sentence,

The sentence you proposed was a good start, but it doesn't answer the
questions I raised above.

Also, ideally I'd like a complete patch: not just the documentation
change, but the .m4 change.  That is, I'd rather not go back to the
old way of doing things, where users could AC_DEFINE any string and
then get into real trouble.  I'd rather have Autoconf check that the
string being defined is in the subset of strings actually supported by

PS.  Another question: is an empty argument list allowed?  That wasn't
clear to me either.

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