C# Pointers

A pointer is a variable that holds the memory address of another type. In C#, pointers can only be declared to hold the memory addresses of value types (except in the case of arrays).

Pointers are declared implicitly, using the symbol *, as in the following example:

int *p;

[Note that some coders place the dereferencer symbol immediately after the type name, eg.

int* p;

This variation appears to work just as well as the previous one.]

This declaration sets up a pointer 'p', which will point to the initial memory address of an integer (stored in four bytes).

The combined syntactical element *p ('p' prefixed by the dereferencer symbol '*') is used to refer to the type located at the memory location held by p. Hence given its declaration, *p can appear in integer assignments like the following:

*p = 5;

This code gives the value 5 to the integer that was initialised by the declaration. It is important, however, not to confuse such an assignment with one in which the derefencer symbol is absent, e.g.

p = 5;

The effect of this assignment is to change the memory location held by p. It doesn't change the value of the integer initialised by the original declaration; it just means that p no longer points to that integer. In fact, p will now point to the start of the four bytes present at memory location 5.

Another important symbol for using pointers is the operator &, which in this context returns the memory address of the variable it prefixes. To give an example of this symbol, the following code sets up p to point to integer i's memory location:

int i = 5;
int *p;
p = &i;

Given the above, the code

*p = 10;

changes the value of i to 10, since '*p' can be read as 'the integer located at the memory value held by p'.

Let us take a look at the following exmple that captures most of the concepts stated above

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
    class Program
        static void Main(string[] args)
 	int x ;

                int x = 100;

                /* The &x gives the memory address of the variable x,
                 * which we can assign to a pointer variable */

                int* ptr = &x;
                Console.WriteLine((int)ptr); // Displays the memory address
                Console.WriteLine(*ptr); // Displays the value at the memory 

Before you will be able to run the above code you will have to change some settings. Go to Projects -> Properties ->Build and check the checkbox against "Allow unsafe code".

If you run the above code, you should see the output something similar to the below.