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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: 'Amalgamated' source code
Date: Tue, 03 Jan 2017 16:26:34 -0800
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Thiago Adams <thiago.adams@gmail.com> writes:
> On Tuesday, January 3, 2017 at 7:36:53 PM UTC-2, Bart wrote:
[...]
>> (But I've just seen one detail I hadn't allowed for, in gcc.c (from 
>> http://people.csail.mit.edu/smcc/projects/single-file-programs/). On 
>> line 733881 in a macro call:
>> 
>> DEF_FORMAT_ATTRIBUTE(PRINTF,1,1_0)
>> 
>> The token '1_0' appears. It starts as a number but presumably must be 
>> treated as alphanumeric.

1_0 is a pp-number, which will result in a syntax error if it survives
preprocessing (assuming you're trying to implement ISO C requirements).

> This did not work for me as well.
>
> #define M(1_0)
>
> M(1)

What did you expect that to do?  If the macro name in a #define is
followed by a '(' with no whitespace, the '( is followed by a list of
macro parameter names, which must be identifiers.  1_0 is not valid in
that context.  "gcc -E" complains:

    error: "1_0" may not appear in macro parameter list

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"