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From: jeff@onion.rain.com (Jeff Beadles)
Newsgroups: comp.sources.wanted,alt.sources.wanted
Subject: Re: What is strdup() supposed to do? Does anyone have a copy?
Message-ID: <1991Feb19.004526.16033@onion.rain.com>
Date: 19 Feb 91 00:45:26 GMT
References: <1991Feb17.045913.17126@sbcs.sunysb.edu> <1991Feb17.164731.7564@onion.rain.com> <1991Feb18.154159.430@persoft.com>
Lines: 65


 In <1991Feb18.154159.430@persoft.com> dag@persoft.com (Daniel Glasser) writes:
 >In article <1991Feb17.164731.7564@onion.rain.com> I wrote:
 >>Here's an updated and working version of strdup()
 >>
 >>char *
 >>strdup (s)
 >>char *s;
 >>{
 >>	static char *rets;
 >>	extern char *malloc();	/* Might be extern void *malloc(); */
 >>	extern int strlen();
 >>
 >>	rets=malloc (sizeof (char) * strlen (s) + sizeof(char) );
 >>
 >>	/* Malloc failed.  Oops! */
 >>	if (!rets) {
 >>		return((char *)0);
 >>	}
 >>
 >>	(void) strcpy (rets, s);
 >>
 >>	return (rets);
 >>}
 >
 >Two minor nits...
 >
 >Nit #1:	Why is rets static?  Is there any reason to not leave it as automatic?
 >        The value is not used between calls, and why waste data space when the
 >	stack is available for these purposes?  I'd suggest leaving the "static"
 >	off.
 
A creature of habit, I suppose.  I've been bitten too often when I return
something from a function that isn't static.  (int's, for example.)  For this
case, it really doesn't matter.

It's kinda like the braces around the malloc failure.  They're not technically
required, but it's not a bad habit. :-)
 
 >Nit #2:	You should simplify your expression in the "malloc()", that is,
 >		sizeof(char) * strlen(foo) + sizeof(char)
 >	could be written
 >		sizeof(char) * (strlen(foo) + 1)
 
 >	I realize that this doesn't make it any less work for the CPU
 >	(both are 1 add and 1 multiply), but to the latter form makes
 >	it clearer what is being done (allocating enough space for
 >	strlen(foo)+1 chars).
 
Untrue.  What if sizeof(char) != 1?  Yours will break, and mine will work.
 
{note:  I don't personally know of places where this isn't true, but then
        again, some people think that sizeof (int) == sizeof (char *) :-}

Also, sizeof() isn't taking anything extra.  It's changed to a '1' by the
COMPILER.  Overall, I stand by my choice of + sizeof(char).



I wrote this as an example for folks needing the functionality, not as a
finely-tuned piece of code.  You're more than welcome to improve on it.

	-Jeff
-- 
Jeff Beadles		jeff@onion.rain.com