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From: deller@vrdxhq.UUCP
Newsgroups: comp.lang.c
Subject: Incrementing of preprocessor symbols
Message-ID: <3424@vrdxhq.UUCP>
Date: Wed, 15-Apr-87 18:39:42 EST
Article-I.D.: vrdxhq.3424
Posted: Wed Apr 15 18:39:42 1987
Date-Received: Fri, 17-Apr-87 05:01:22 EST
Organization: Verdix Corporation, Chantilly, VA
Lines: 36
Keywords: C #define

Help please. We have a program in which we would like to use something like:

  assert( <expr> ) ;

and have it expand to

  if ( ! <expr> ) error_call( <n>, __FILE__, __LINE__ ) ;

(the __FILE__ and __LINE__ are preprocessed into a quoted string that is the 
filename being compiled, and an integer that is the line number, in the source,
where the symbol appears).

Everything is quite easy to do with a #define, except the handling of <n>.  We
would like the <n> to increment with each expansion encountered in the source,
i.e. with each "assert" in the text.  The <n> helps distinguish the different 
assertions on VMS, where C does not expand __FILE__ and __LINE__ as it does on 
Sun, Sequent, VAX UNIX, and VAX Ultrix.

So, the problem is how to get an <n> that increments with each usage in the
source.  Note that <n> should NOT be incremented each time the statment is
encountered during execution; a lexical increment is desired.

We are not looking to use a pre-preprocessor that modifies the sources as they 
are fed to the "cc" command (piping the source messes up __FILE__, and we can't
afford the extra time to make file copies); we are looking for a solution 
entirely within the C preprocessor.

I would note that any self-respecting macro facility for any assembler can do 
this sort of thing with its eyes closed and one macro expansion behind its 
back.  If as I am beginning to suspect, this is not possible with C, then 
perhaps the C standards committee might take note.

Steven Deller
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