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From: chris@mimsy.UUCP
Newsgroups: comp.unix.wizards
Subject: Re: Ultrix-2.0 calloc bug?
Message-ID: <8899@mimsy.UUCP>
Date: Sat, 3-Oct-87 13:02:58 EDT
Article-I.D.: mimsy.8899
Posted: Sat Oct  3 13:02:58 1987
Date-Received: Sun, 4-Oct-87 06:54:39 EDT
References: <12300001@silver>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 45

In article <12300001@silver> ferneau@silver.bacs.indiana.edu writes:
>I am having a problem with dynamic memory allocation on silver (a
>VAX 8650 running Ultrix 2.0) using the calloc() routine, which seems
>to be corrupting my array.

The bug is in your program, not in calloc() (which is not to say
that there cannot be a bug in calloc() too).

Everything up to the following looks fine after a quick scan; then:

>char **
>replicate(ac,av)
>int ac;
>char **av;
>{
>  char **nav;
>  int x;
>  
>  if ((nav = (char **) calloc(ac,sizeof(char *)))==NULL) {

It is good that you test the return value; you also, however, need
to declare `calloc' as `char *calloc()', or, in dpANS C:

	char *calloc(int nitems, unsigned int itemsize);

(note that I prefer to name the arguments so that someone scanning
the declaration can see what the seventh `int' is for.)

Moving along:

>  for (x=0; x<ac; x++) {
>    if ((nav[x]=(char *)calloc(sizeof(av[x])+1,1))==NULL) {

Here is the bug.  `sizeof av[x]' is the size of `char *', not the
length of the string stored in that particular `char *'.  Make
this

    if ((nav[x] = calloc(strlen(av[x])+1, sizeof(char))) == NULL) {

(the cast no longer being needed, and `sizeof(char)' being a hedge
against `char' perhaps being multi-byte, and as a bit of documentation)
and the program should work.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris