From: Erik Max Francis <max AT alcyone DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: How assign to NULL POINTER
Date: Wed, 13 Nov 1996 09:03:25 -0800
Organization: Alcyone Systems
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Message-ID: <3289FF5D.6C1E38FA@alcyone.com>
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To: djgpp AT delorie DOT com
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Ole Winther wrote:

> I where asking about course of "segment violation at pointer " error, while
> running a gcc compiled program. I got the answer that it probaly is a Null
> pointer assignment and I must belive it'sw true, course the "BC" compiled
> program which where running the same code, was also complaining about the
> Null pointer assignment while program end was ended.
> 
> I really dont know how I can assign value's to the NULL pointer, can someone
> describe how this can be done?

"Null pointer assignment" means you're dereferencing a null pointer and
attempting to write to where it's pointing.  This is a bad thing.

That is, 

    int *p = 0;

    *p = 26;

is a null pointer assignment.

Generally intermittent crashes and such are the cause of "dangling pointers"
(sometimes also called null pointer assignment), where the pointer isn't
necessarily a null pointer, but it is not pointing at well-behaved memory.
For instance, 

    int *p;

    *p = 23;

is a dangling pointer assignment; the pointer p is not initialized, and thus
initially contains garbage.  This could be null, or it could be pointing at
some random location in memory.

-- 
                             Erik Max Francis | max AT alcyone DOT com
                              Alcyone Systems | http://www.alcyone.com/max/
                         San Jose, California | 37 20 07 N 121 53 38 W
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