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From: blodgett@apollo.HP.COM (Bruce Blodgett)
Newsgroups: comp.lang.c,comp.std.c
Subject: Re: Just a minor new twist on free()
Message-ID: <4d5780ad.20b6d@apollo.HP.COM>
Date: 11 Oct 90 22:55:00 GMT
References: <PDS.90Oct8101336@lemming.webo.dg.com>
Sender: root@apollo.HP.COM
Lines: 17
In-reply-to: pds@lemming.webo.dg.com's message of 8 Oct 90 14:13 GMT


If you are trying to compile code which may call free() with a NULL
argument, and use an implementation of free() that does not handle NULL
gracefully, try adding one of the following to <stdlib.h>:

#define free(x) ( (x) ? free(x) : ( (void)0 ) )
  or
#define free(x) { void * ptr = (x); if ( ptr != NULL ) free(ptr); }

The former has the side-effect of evaluating the argument to free()
twice.  The latter is a statement rather than an expression of type
void, and therefore wouldn't work if someone tried to embed a call to
free() in an expression (there are not many uses for subexpressions of
type void).
Bruce Blodgett
blodgett@apollo.hp.com
(508) 256-0176 x4037