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From: gwyn@smoke.brl.mil (Doug Gwyn)
Newsgroups: comp.lang.c
Subject: Re: calloc and realloc semantics
Keywords: calloc realloc
Message-ID: <15084@smoke.brl.mil>
Date: 5 Feb 91 19:50:57 GMT
References: <4865@cui.unige.ch>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 20

In article <4865@cui.unige.ch> afzal@cui.unige.ch (Afzal Ballim) writes:
>Is it safe (and portable) to use realloc to resize an array that
>was generated using calloc?

calloc() is supposed to be simply an interface to malloc() that also
fills the allocated storage with 0-valued bytes.  Thus it isn't very
useful, but it should be safe to use in conjunction with other functions
in the malloc() family.

>... After the realloc, what is the status of array1?

If array2 is a null pointer, then array1 should still points to the
same data (and same-sized allocation) as before; otherwise, array1 is
now an invalid pointer and should not be further used.  In the latter
case, you must use array2 to access the (possibly moved) data.

>Is this use of newsize*sizeof(element) valid?  I am worried here about
>alignment of elements. 

Yes, there is no problem with that.