C# 0 The Complete Reference

/unsafe

 compiler option.

Since pointers are at the core of unsafe code, we will begin there.

Pointer Basics

A pointer is a variable that holds the address of some other object, such as another variable. 

For example, if 

x

 contains the address of 

y

, then 

x

 is said to “point to” 

y

. When a pointer 

points to a variable, the value of that variable can be obtained or changed through the pointer. 

Operations through pointers are often referred to as 

indirection.

Declaring a Pointer

Pointer variables must be declared as such. The general form of a pointer variable 

declaration is

type

*

var-name

;

Here, 

type

 is the pointer’s 

referent type,

 which must be a nonreference type. Thus, you cannot 

declare a pointer to a class object. A pointer’s referent type is also sometimes called its 

base

type.

 Notice the placement of the 

*

. It follows the type name. 

var-name

 is the name of the 

pointer variable.

Here is an example. To declare 

ip

 to be a pointer to an 

int

, use this declaration:

int* ip;

For a 

float

 pointer, use

float* fp;

In general, in a declaration statement, following a type name with an 

*

 creates a pointer type.

The type of data that a pointer will point to is determined by its referent type. Thus, in 

the preceding examples, 

ip

 can be used to point to an 

int

, and 

fp

 can be used to point to a 

float

. Understand, however, that there is nothing that actually prevents a pointer from 

pointing elsewhere. This is why pointers are potentially unsafe.

If you come from a C/C++ background, then you need to be aware of an important 

difference between the way C# and C/C++ declare pointers. When you declare a pointer 

type in C/C++, the 

*

 is not distributive over a list of variables in a declaration. Thus, in 

C/C++, this statement

int* p, q;

declares an 

int

 pointer called 

p

 and an 

int

 called 

q

. It is equivalent to the following two 

declarations:

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