Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!van-bc!eslvcr!hasvcr!ted
From: ted@hasvcr.UUCP (Ted Powell)
Newsgroups: comp.lang.fortran
Subject: Re: Using cpp for macro substitution.
Summary: Avoid special characters cheaply by post-processing with tr
Keywords: cpp, tr
Message-ID: <194@hasvcr.UUCP>
Date: 10 Jul 90 17:47:15 GMT
References: <1990Jul6.162153.17644@helios.physics.utoronto.ca>
Reply-To: ted@hasvcr.wimsey.bc.ca (Ted Powell)
Distribution: na
Organization: H.A. Simons Ltd., Vancouver, BC
Lines: 48

In article <1990Jul6.162153.17644@helios.physics.utoronto.ca> quinlan@physics.utoronto.ca (Gerald Quinlan) writes:
>I have a question about using the C preprocessor to perform macro
>substitutions in a Fortran program. ...
[example omitted]
>Note how cpp has combined all the statements of the macro into one long line.
>I suppose this isn't a problem in C, where the statements end with ";" and
>more than one statement per line is allowed.  But in Fortran this doesn't
>work; the compiler won't accept adtest.f.  Does anyone know how to get
>around this?  I've tried various tricks to get the macro inserted properly,
>but can't seem to find anything that works.

Your problem is that you want to get characters into the macro expansion
that cpp considers special. An unescaped newline terminates the macro
definition, rather than being included in it, and consecutive spaces
are reduced to a single space.

Pick a couple of characters that do not otherwise occur in your source
files, for example percent to represent newline and underscore to
represent space. Then (assuming you are in a Unix environment; you'll
have to use an intermediate file otherwise) pipe the output of cpp
through:
		tr '_%' ' \012'
			 ^note space

This translates underscores into spaces and percent signs into newlines
(\012 is interpreted by tr as a newline character). Note that some
versions of the tr program require their arguments in a slightly
different form--check your manual if necessary.

Your macros now look something like:
	#define qqsv(a,b,c) line one\
	%______line two\
	%______line three\
	%______last line
	^column 1

The remainder of your program is of course unchanged, since actual
spaces and newlines are unaffected by their trip through tr.

All this takes much less time to do than to describe, of course.

M4 is a nice language. I used a similar language called UMIST heavily
for many years as a Fortran preprocessor, and as an MVTAB (multivariate
contingency tabulator) preprocessor. But in your circumstances I think
M4 is overkill.

-- 
ted@hasvcr.wimsey.bc.ca   ...!ubc-cs!van-bc!hasvcr!ted    (Ted Powell)