Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!yale!mintaka!spdcc!ima!haddock!karl
From: karl@haddock.ima.isc.com (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: Why 'life after free'.
Keywords: question about malloc+free combination.
Message-ID: <18363@haddock.ima.isc.com>
Date: 2 Oct 90 02:20:59 GMT
References: <quan.654673946@sol>
Reply-To: karl@kelp.ima.isc.com (Karl Heuer)
Distribution: comp
Organization: Interactive Systems, Cambridge, MA 02138-5302
Lines: 19

In article <quan.654673946@sol> quan@sol.surv.utas.oz (Stephen Quan) writes:
>I normally do what you suggest, the reason why a brought up this issue is
>that if what I propose wasn't so unpredictable then I can have something
>like :
>  printf("%s\n",funny('c'));
>  printf("%s\n",funny('x'));

Bad idea, even under the old rules.  This depends on the funny-buffer
retaining its contents until printf() copies it into the stdio buffer.
So it will break if malloc() is called by printf() or any of the stdio
routines it calls--which is sometimes the case.

I generally recommend
	temp = funny('c');  printf("%s\n", temp);  free(temp);
instead.  If you have enough of these that it's painful, consider writing
your own allocation package on top of malloc()/free(), and include a function
that will garbage collect the temporaries.  Shouldn't be difficult.

Karl W. Z. Heuer (karl@kelp.ima.isc.com or ima!kelp!karl), The Walking Lint