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Pointer Help

Pointer Help, Don't understand pointers....

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NelsonTT	6 Oct, 2008 - 04:48 PM Post #1
New D.I.C Head Joined: 5 Oct, 2008 Posts: 16 My Contributions	Hi, it's me again and I need help understanding pointers... From what I understand, pointers are objects that hold memory addresses. & returns a memory address. I don't understand what the * operator does. My questions are: How are pointers useful? What does the * operator do? How does the following program work? CODE #include <iostream> using namespace std; int main() { int total, val; int ptr; total = 3200; ptr = &total; val = ptr; cout << "Total is: " << val << '\n'; return 0; } Thanks in advance!
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NelsonTT	6 Oct, 2008 - 07:16 PM Post #2
New D.I.C Head Joined: 5 Oct, 2008 Posts: 16 My Contributions	Anyone going to answer this?
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JackOfAllTrades

7 Oct, 2008 - 04:36 AM

Post #3

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The * operator is the dereferencing operator. It goes to the memory address at the location and returns the contents of that memory location as the type associated with the pointer. See my comments in the code below.

cpp

#include <iostream>
using namespace std;

int main()
{
     // Let's say total gets a memory address of 0x1000, 
     // val gets a memory address of 0x2000
     int total, val;

     // And ptr gets a memory address of 0x3000
     int *ptr;

     // The memory at location 0x1000 is set to 3200.
     total = 3200;

     // The address of total, 0x1000, is written to the memory 
     // location at 0x3000
     ptr = &total;

     // The memory at location 0x3000 is read and found to 
     // point to memory location 0x1000. The value at memory 
     // location 0x1000 is copied to the memory location 0x2000.
     val = *ptr;

     cout << "Total is: " << val << '\n';

     return 0;
}

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KYA	7 Oct, 2008 - 05:46 AM Post #4
#include <nerd.h> Joined: 14 Sep, 2007 Posts: 4,176 Thanked 48 times Dream Kudos: 1150 My Contributions	Pointers are useful because they allow you yo access variables by reference. When a normal variable is passed in to a function as a parameter, a copy of it is made and used for all functions within the method. This is fine if you're simply returning the end result of that, but often one will want to directly modify the value passed in. So we create a pointer as a parameter and pass in a reference of the variable. Pointers are powerful, elegant, and quite often a pain in the ass if used incorrectly
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NelsonTT	7 Oct, 2008 - 08:37 AM Post #5
New D.I.C Head Joined: 5 Oct, 2008 Posts: 16 My Contributions	Thanks everyone!! I sorta understand pointers now...
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Bench	7 Oct, 2008 - 01:53 PM Post #6
D.I.C Addict Joined: 20 Aug, 2007 Posts: 600 Thanked 8 times Dream Kudos: 150 Expert In: C/C++ My Contributions	Have a look at this article about pointers on Eternallyconfuzzled http://www.eternallyconfuzzled.com/tuts/la...t_pointers.aspx And another one here http://www.daweidesigns.com/cgi-bin/pointers.php Edit: Here's an FAQ on pointers from the C-FAQ website (everything contained here is for C, but nearly all of it also applies to C++ ) http://www.c-faq.com/ptrs/index.html This post has been edited by Bench: 7 Oct, 2008 - 01:59 PM
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