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From: mcdonald@aries.scs.uiuc.edu (Doug McDonald)
Newsgroups: comp.lang.c
Subject: Re: realloc() (was: Re: Safe coding practices)
Message-ID: <1991Jan30.201955.21797@ux1.cso.uiuc.edu>
Date: 30 Jan 91 20:19:55 GMT
References: <1991Jan30.193308.3897@athena.mit.edu> <23975:Jan2516:36:5891@kramden.acf.nyu.edu> <1991Jan30.121425.16882@unhd.unh.edu>
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Organization: University of Illinois at Urbana
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In article <1991Jan30.193308.3897@athena.mit.edu> jik@athena.mit.edu (Jonathan I. Kamens) writes:
>
>  I believe that if the realloc() fails, the memory block pointed to by the
>pointer passed into realloc() is no longer guaranteed to be valid.  Therefore,
>Jaeschke is right -- after realloc() returns NULL, you should not try to use
>the block whose address you passed into realloc().
>

"
void *realloc(void *p, size_t size);

realloc changes the size of the object pointed to by p to size. The
contents will be unchanged up to the minimum of the old and new sizes.
If the new size is larger the new space is uninitialized. Realloc returns
a pointer to the new space, or NULL if the request cannot be satisfied,
in which case *p is unchanged."

The "" indicate a quote from K&R II. Note the last sentence: it says that
*p is unchanged. *p is the CONTENTS of what p originally (and presumably still 
must) point to.


So the quote preceeded by > signs is not true for a correct realloc.
You CAN reuse p and *p after a failed realloc.


Doug McDonald