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From: rbutterworth@orchid.UUCP
Newsgroups: comp.lang.c
Subject: Re: #if inside #define -- easy to do, but is it a good idea?
Message-ID: <10898@orchid.waterloo.edu>
Date: Tue, 29-Sep-87 14:24:40 EDT
Article-I.D.: orchid.10898
Posted: Tue Sep 29 14:24:40 1987
Date-Received: Thu, 1-Oct-87 01:11:39 EDT
References: <157@decvax.UUCP> <29339@sun.uucp>
Organization: U of Waterloo, Ontario
Lines: 33

In article <29339@sun.uucp>, david@sun.uucp (David DiGiacomo) writes:
> In article <157@decvax.UUCP> minow@decvax.UUCP (Martin Minow) writes:
> >From time immemorial, C has forbidden # control lines inside a
> >macro definition.
> It would be a nice feature to have, but it's not really necessary for your
> example

OK, here's a real example where it would be useful
(in fact I can't see any nice way of doing this without the ability):

    #if !defined(compiler_A)
    #if !defined(compiler_B)
    #if !defined(compiler_C)
    ^%$%^#^%$&^% syntax error since we don't know this compiler.

    #else  /* compiler_C */
    #   define ARGSUSED /*ARGSUSED*/
    #endif /* compiler_C */

    #else  /* compiler_B */
    #   define ARGSUSED #argsused
    #endif /* compiler_B */

    #else  /* compiler_A */
    #   define ARGSUSED #pragma argsused
    #endif /* compiler_A */

goes into a header file, and a program can simply use the manifest
ARGSUSED
in the appropriate places.

Without this ability, the source gets rather ugly if it is to run
on all three compilers.