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From: vinoski@apollo.HP.COM (Stephen Vinoski)
Newsgroups: comp.lang.c,comp.std.c
Subject: Re: Question on ANSI ## pre-processor operator.
Message-ID: <51951216.20b6d@apollo.HP.COM>
Date: 15 May 91 19:27:00 GMT
References: <28302040.69ED@deneva.sdd.trw.com> <519416cd.20b6d@apollo.HP.COM>
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Reply-To: vinoski@apollo.HP.COM (Stephen Vinoski)
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Organization: Hewlett-Packard Apollo Division - Chelmsford, MA
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In article <519416cd.20b6d@apollo.HP.COM> vinoski@apollo.HP.COM (Stephen Vinoski) writes:
>In article <28302040.69ED@deneva.sdd.trw.com> knurlin@spf.trw.com (Scott Karlin) writes:
>>I am looking for a clarification on the ANSI-C token merging
>>operator (##).  According to H&S:  "After *all* [emphasis mine]
>>macro replacements have been done, the two tokens surrounding
>>any ## operator are combined into a single token."  I interpret
>>this to mean that:
>>
>>#define INDEX 0
>>#define FN_NAME(x) name ## x
>>void FN_NAME(INDEX) () { printf("Hello\n"); }
>
>I had a problem with token pasting similar to yours.  A compiler
>writer said that the problem was caused by the fact that I was
>attempting to paste arbitrary text with macro parameters; he said that
>token pasting is only meant to work on macro parameters.
>
>The ANSI C standard appears to agree with him; I believe it is section
>3.8.3.3 (I don't have the standard handy) that says that ## causes
>macro parameters to be pasted together.  If I have misinterpreted the
>standard, I'm sure I will hear about it.  :-)

Well, what do you know - I *did* misinterpret the standard.  Sigh.
Section 3.8.3.3 states that preprocessor tokens can be pasted
together.  The problem knurlin@spf.trw.com has is caused by the fact
that token pasting occurs before the result is rescanned for further
macro replacement.  Thanks to steven@pacific.csl.uiuc.edu (Steven
Parkes) for setting me straight on this one.

I hereby promise not to quote the standard from memory again.


-steve

| Steve Vinoski  (508)256-0176 x5904       | Internet: vinoski@apollo.hp.com  |
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