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From: darrylo@hpsrlc.HP.COM (Darryl Okahata)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Turbo C memset problem
Message-ID: <3320068@hpsrlc.HP.COM>
Date: Sat, 14-Nov-87 20:03:53 EST
Article-I.D.: hpsrlc.3320068
Posted: Sat Nov 14 20:03:53 1987
Date-Received: Mon, 16-Nov-87 04:50:13 EST
References: <238@cunixc.columbia.edu>
Organization: HP Network Measurements Div - Santa Rosa, CA
Lines: 41

In comp.sys.ibm.pc, nwc@cunixc.columbia.edu (Nick Christopher) writes:

> I had code that was very happy in the small model in which I blanked and
> character array using memset as follows:
> 
> char string[80]
> 
> memset(string,NULL,80);
> 
> however when I moved to large model this no longer worked, it began to have
> the exact same 3 garbage characters at the begining of string.  Is this the 
> fault  of my format or the memset's fault.
> 
> /nwc
> -- 
> 		"I am the Lorvax. I speak for the machines."
> ______________________________________________________________________________
> nwc%cunixc@columbia, columbia!cunixc!nwc  BITNET: nwcus@cuvma 
>             USENET: topaz!columbia!cunixc!nwc
> ----------

     The second argument to memset() is supposed to be a character: in
place of a character, you have "NULL" which typically represents a NULL
pointer (strictly speaking, a null pointer should be "(char *) NULL", not
just "NULL" -- but that's another story).  To fix your problem, use:

     memset(string, '\0', 80);

Your problem stems from the use of "NULL" instead of a character; in the
small memory model, the use of "NULL" pushes a word (16 bits) onto the
stack for the second argument, whereas, in the large memory model, two
words, instead of just one, are pushed on the stack.  As a result, the
stack was misaligned, and memset() could not properly access its arguments.

     -- Darryl Okahata
	{hplabs!hpccc!, hpfcla!} hpsrla!darrylo
	CompuServe: 75206,3074

Disclaimer: the above is the author's personal opinion and is not the
opinion or policy of his employer or of the little green men that
have been following him all day.