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From: levy@ttrdc.UUCP (Daniel R. Levy)
Newsgroups: net.unix
Subject: Re: strdup
Message-ID: <1170@ttrdc.UUCP>
Date: Mon, 1-Sep-86 23:58:21 EDT
Article-I.D.: ttrdc.1170
Posted: Mon Sep  1 23:58:21 1986
Date-Received: Tue, 2-Sep-86 21:30:10 EDT
References: <3325@brl-smoke.ARPA> <241@bsdpkh.UUCP>
Organization: AT&T, Computer Systems Division, Skokie, IL
Lines: 37

In article <241@bsdpkh.UUCP>, heff@bsdpkh.UUCP (Paul K Heffner) writes:

>> /* hjb 08/25/86 */
>> char * strdup(s)
>> char *s;
>> {
>> 	char *p;
>> 	extern char *malloc();
>> 	if(p=malloc(strlen(s)+1)) strcpy(p,s);
>> 	return p;
>> }

>The above code doesn't return a null if malloc fails

It DOESN'T???  Gee, then maybe you have a busted malloc().  If malloc()
fails, it should return the null pointer.  That is what is being tested in
the clause 'if(p=malloc(strlen(s)+1))'.  As so many people have expounded
in net.lang.c:  a null pointer is semantically the same as zero in the C
language (except for sizeof(), should pointers exist of sizes other than
sizeof(int)).

So if malloc() fails, p gets NULL and the return value is likewise NULL.
The if() simply keeps strcpy from trying to copy something into an invalid
buffer ("pointed to" by NULL) should malloc() fail.  Then the user can catch
the error instead of the program dumping core.  Simple huh?

>
>						Paul Heffner
>					{ihnp4,akgua,attmail}!bsdpkh!heff
-- 
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| at&t computer systems division |  upon which I may hack.
|        skokie, illinois        |
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