C# Pointers

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 ; unsafe { 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 Console.ReadLine(); } } }

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. 

69725392 100