From: "Edmund Horner" <ejrh AT paradise DOT net DOT nz>
Newsgroups: comp.os.msdos.djgpp
References: <s269qsgaqr5446ot429cat1q8vo7rq5t9c AT 4ax DOT com>
Subject: Re: memset    behavior
Lines: 52
X-Priority: 3
X-MSMail-Priority: Normal
X-Newsreader: Microsoft Outlook Express 5.00.2919.6600
X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2919.6600
Organization: Paradise Net
Message-ID: <967089732.935725@shelley.paradise.net.nz>
Cache-Post-Path: shelley.paradise.net.nz!unknown AT 203-96-154-214 DOT tnt7 DOT paradise DOT net DOT nz
X-Cache: nntpcache 2.4.0b5 (see http://www.nntpcache.org/)
Date: Thu, 24 Aug 2000 16:03:37 +1200
NNTP-Posting-Host: 203.96.152.26
X-Complaints-To: newsadmin AT xtra DOT co DOT nz
X-Trace: news.xtra.co.nz 967089752 203.96.152.26 (Thu, 24 Aug 2000 16:02:32 NZST)
NNTP-Posting-Date: Thu, 24 Aug 2000 16:02:32 NZST
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com

"Radical NetSurfer" <radsmail AT juno DOT com> wrote in message
news:s269qsgaqr5446ot429cat1q8vo7rq5t9c AT 4ax DOT com...
> I had a line of code like this:
>
> char buffer[100];
> printf("%d %s\n",  (char*)memset(buffer, '-', 64));
>
> and what was discovered is:
>
>        IF buffer already contains a string,  "ABCD",
> THEN memset() as above printed:
>
> "-------------------------------------------------------------BCD"
> (truncated to fit here)
>
> OBSERVE: that the everything was MOVED DOWN
>       THEN:  the dashed-line added.
>
> QUESTION: Why would this be ?

You're in big trouble here!

1. Your printf comes with %d and %s, but you only provide one argument
(memset's return value)!  Perhaps the %d was a typo.
2. You can't rely on being able to use blocks of memory as strings!  The
results will depend on the next 0 byte encountered, and unless you're
explicitly going to have one, your string could be any length at all -- and
your program will misbehave.

Thanks to the above, there is no defined behaviour for this program.

> PROBLEM #2:
> There's no such thing as a    memcat()  routine...
> why?  How can binary data (data containing 0x00) be
> CONCATED to accurately and properly return the
> size (pointer growth) of a buffer?
>
> (growing_pointer *)memcat(destination, source, n_bytes);
>
> such that "growing pointer" is simply something that provides
> the buffer address of 'source', and its length.
>
> Any ideas here?

Since a pointer doesn't know anything about the size of the data it's
pointing to, memcat would probably need to use a terminating 0 byte -- just
like strcat does.  Try strcat.  Better still -- figure out exactly what it
is you want to do with your data!

Edmund.