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Message-ID: <43579BEF.9010704@byu.net>
Date: Thu, 20 Oct 2005 07:30:23 -0600
From: Eric Blake <ebb9 AT byu DOT net>
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To: community help <helpcomm AT yahoo DOT com>
CC: cygwin AT cygwin DOT com
Subject: Re: problem with g++ on cygwin
References: <20051020130601 DOT 82903 DOT qmail AT web30005 DOT mail DOT mud DOT yahoo DOT com>
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According to community help on 10/20/2005 7:06 AM:
> Hi,
> 
> I'm using g++ on cygwin for developping some c++
> programs.
> 
> I noticed that everytime i manipulate pointers i have
> an error saying:
> "Segmentation Fault <Core Dumped>".

Well, it's because you are trying to modify read-only memory.  Fix the bug
in your code.  Your problem is not cygwin-specific, although cygwin is a
little less forgiving of memory usage errors, and more likely to core dump
when your code is buggy.

> ----------------------
> #include <iostream.h>
> #include <string.h>
> 
> int main()
> {
> 	char * str;
> 	str = "hello";

The type of "hello" is const char*, because it lives in read-only memory.
 You are (silently) casting away the const, and that is your bug; compile
with -Wall and you should be getting a warning.

> 	*(str+1) = 'a';

Oops - now you are trying to change a read-only location.

Now, had you declared this instead:
char str[] = "hello";

Then *(str+1) = 'a' is legal, because C++ allows a char[] initializer to
copy the contents of a string literal, without putting it in read-only memory.

- --
Life is short - so eat dessert first!

Eric Blake             ebb9 AT byu DOT net
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