Pointers

A pointer is a variable that stores a memory address as its value. Usually, we use to store the memory address of some other variable. We say that it points to the address of that variable.

Declaration of a pointer

A pointer is declared using the * operator. The generic syntax with no assignment is.

type* pointer_name;

Note

It’s perfectly legitimate to write the following also: type *pointer_name;

Assigning an address to a pointer

Say we have a variable named my_variable and we want to create a pointer named pointer_to_my_variable to its address. Generically, we can do this by

type1 my_variable = some_value;
type1 *pointer_to_my_variable = &my_variable;

Two things to note here:

1. Our pointer must have the same type as the variable.

2. The & operator extracts the address of the variable when applied to the my_variable.

Note

The &-operator is sometimes called the “reference” operator. The *-operator is on the other hand called the “dereference” operator.

A concrete example:

double x = 2; //x is assigned the value 2.
double *pointer_to_x = &x; //ptr stores the memory address of x.

Extracting a value from a pointer

The pointer stores the memory address of a variable as its value. But we can still extract the value of a variable from the pointer itself! This is known as dereferencing and is facilitated by the * operator as follows:

type1 variable_value = *pointer_to_variable;

Expanding the example from the last section:

double x = 2; //x is assigned the value 2.
double *pointer_to_x = &x; //x_ptr stores the memory address of x.

double x_value = *pointer_to_x; //Dereference pointer_to_x (extract value of x).