Declaring Pointers

Since we are covering the use of variables, it is worth explaining the syntax used to define pointers and arrays because there are some potential pitfalls. Chapter 2, Working with Memory, Arrays, and Pointers, covers this in more detail, so we will just introduce the syntax so that you are familiar with it.

In C++, you will access memory using a typed pointer. The type indicates the type of the data that is held in the memory that is pointed to. So, if the pointer is an (4 byte) integer pointer, it will point to four bytes that can be used as an integer. If the integer pointer is incremented, then it will point to the next four bytes, which can be used as an integer.

In C++, pointers are declared using the * symbol and you access a memory address with the & operator:

    int *p; 
    int i = 42; 
    p = &i;

The first line declares a variable, p, which will be used to hold the memory address of an integer. The second line declares an integer and assigns it a value. The third line assigns a value to the pointer p to be the address of the integer variable just declared. It is important to stress that the value of p is not 42; it will be a memory address where the value of 42 is stored.

Note how the declaration has the * on the variable name. This is common convention. The reason is that if you declare several variables in one statement, the * applies only to the immediate variable. So, for example:

    int* p1, p2;

Initially, this looks like you are declaring two integer pointers. However, this line does not do this; it declares just one pointer to integer called p1. The second variable is an integer called p2. The preceding line is equivalent to the following:

    int *p1;  
    int p2;

If you wish to declare two integers in one statement, then you should do it as follows:

    int *p1, *p2;