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From: rh@smds.UUCP (Richard Harter)
Newsgroups: comp.lang.c
Subject: Re: Using Macros
Summary: do {body} while(0)
Message-ID: <151@smds.UUCP>
Date: 8 Aug 90 03:33:26 GMT
References: <14339@shlump.nac.dec.com> <manning.650051935@gap>
Organization: SMDS Inc., Concord, MA
Lines: 21

Sigh.  I will probably be one of many posting this, but this seems
to have already generated some confusion.  Shouldn't this be in
the "most frequently asked questions" posting?

If you have a block of statements defined in a macro which you
wish to use as though it were a function, there are several ways
to handle it.  Perhaps the clearest is:

#define A_MACRO(args) do {...body...} while(0)

This makes A_MACRO a statement.  This protection is needed when
you have A_MACRO in an if statement, e.g.

if (foo==bar) A_MACRO(moby);
else B_MACRO(gumby);

-- 
Richard Harter, Software Maintenance and Development Systems, Inc.
Net address: jjmhome!smds!rh Phone: 508-369-7398 
US Mail: SMDS Inc., PO Box 555, Concord MA 01742
This sentence no verb.  This sentence short.  This signature done.