RE: Beginner question

[Kevin Wolfskill <kevin.wolfskill@jadesolutions.com>]

The one thing to be aware of with pointers is that since you are directly
addressing memory, you can actually change some portion of memory which is
not what you thought  it was.  That sounds confusing, but happens when you
use a pointer which hasn't been initialized before you use it (i.e. make
sure you set where the pointer points to (ptrTemp = new XZY), before setting
or reading the value the pointer points to (*ptrTemp = 43 or abc =
*ptrTemp).  The other common problem with pointers is when you increment
them beyond the end of their allocated memory space, or decrement them be
before  the beginning of their allocated memory space (i.e.
char *ptrTemp = New int[2];

*ptrTemp++ = 12; // This is OK, we just set the first element to 12, and
have ptrTemp pointing to the second element
*ptrTemp++ = 34; // This is OK to set the value of the second to 34, but now
ptrTemp points to a third elelment which we didn't allocate
*ptrTemp = 56; // This is BAD because we just set the value of a third
element, but only allocated two elements, so we just wrote on top of some
other data...

Both unitialized pointers and pointing off the end of allocated memory can
be extremely hard bugs to track down.  So, just be careful, and try to make
sure that you don't let these bugs into your code.  Pointers are like cars,
when used properly, they are pretty much indispensible, but when used wrong,
they can cause big problems.

Good Luck and Have Fun!!!

Kevin Wolfskill
JADE Solutions
Office US   (303) 448-1019 ext. 23
Fax US      (303) 449-1548
Kevin.Wolfskill@jadesolutions.com
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-----Original Message-----
From: Frag_ Daddy [mailto:frag_daddy_@hotmail.com]
Sent: Friday, June 09, 2000 11:54 PM
To: gameprogrammer@gameprogrammer.com
Subject: Re: Beginner question




     You seem to have a basic understanding of what they are.  Yeah, they 
just point to a certan spot in the memory, but they have a lot of 
advantages.  For one, they can point to an array or something, so they don't

have to be just one object (kind of).  Also, they can just have a block of 
memory allocated (via malloc(...) or new).  This greatly improves the 
flexibility of C++.  This doesn't explain it too well, but I hope it helps a

little.



>From: wegifford <wegifford@GRUMPY.FORTLEWIS.EDU>
>Reply-To: gameprogrammer@gameprogrammer.com
>To: gameprogrammer@gameprogrammer.com
>Subject: Beginner question
>Date: Thu, 08 Jun 2000 20:28:51 -0600
>
>Hey there,
>    I am a beginner and I am covering pointers and have a few questions.  
>The
>book I am using is not giving me the best explanation.  The code makes tons

>of
>sense but I want to know a little more about what a pointer is.
>    As I understand it a pointer variable is pointing to a variable 
>location in
>memory.  So when passed in a function it is not exactly being passed but 
>where
>the variable is located is being pass. What is a pointer exactly used for?

>Is
>the previous explantion the answer.  If so when is the best time to declare
>and use pointers? What is a benefit of a pointer? Is it just speed?  Any 
>help
>you all could give would shed light on this concept.
>
>                                                         William
>
>
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We were all beginners once

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