Pointers Are Variables

Data Structures and Algorithms with Object-Oriented Design Patterns in C++

Pointers Are Variables

The C++ statement

int* p;

declares a pointer . A pointer is a variable the type of which has the form

where T is an arbitrary type. In this case,

and we say that p is a pointer to int.

Since a pointer is a variable, it has all the attributes of a variable. In particular, it has both an address (l-value) and a value (r-value).

Consider a C++ program that contains the following global variable declarations:

int i = 57;
int j = 31;
int* p = 0;
int* q = (int*) 1004;

Suppose the four variables, i, j, p and q, are stored in contiguous memory locations starting at address 1000 as shown in Figure

. (We assume that

). Note that the variable named j has the value 31 and is found at address 1000. Similarly, the variable named q has the value 1004 and is found at address 1012.

Figure: Memory Layout of C++ Variables and Pointers

An assignment statement such as

i = j;

takes the value (r-value) of j, in this case 31, and stores it in memory at the address (l-value) of i, in this case 1000. Similarly, the assignment

p = q;

takes the value of q, in this case 1004, and stores it in memory at the address of p, in this case 1008.

Dereferencing Pointers