Pointers Operators

The &, or address operator, is a unary operator that returns the address of its operand. For example, assuming the definitions

int y = 5;

int *yPtr;

the statement

yPtr = &y;

assigns the address of the variable y to pointer variable yPtr. Variable yPtr is then said to “point to” y. Figure shows a schematic representation of memory after the preceding assignment is executed.

Figure

The figure shows the representation of the pointer in memory, assuming that integer variable y is stored at location 600000, and pointer variable yPtr is stored at location 500000. The operand of the address operator must be a variable; the address operator cannot be applied to constants, to expressions or to variables declared with the storage class register.

The unary * operator, commonly referred to as the indirection operator or dereferencing operator, returns the value of the object to which its operand (i.e., a pointer) points. For example, the statement

printf( "%d", *yPtr ); prints the value of variable y, namely 5 in figure. Using * in this manner is called dereferencing a pointer.

Dereferencing a pointer that has not been properly initialized or that has not been assigned to point to a specific location in memory is an error. This could cause a fatal execution time error, or it could accidentally modify important data and allow the program to run to completion with incorrect results.

Example

/*Using the & and * operators */
#include <stdio.h>
.
int main( void )
{
int a; /* a is an integer */
int *aPtr; /* aPtr is a pointer to an integer */

a = 7;
aPtr = &a; /* aPtr set to address of a */

printf( "The address of a is %p"
"\nThe value of aPtr is %p", &a, aPtr );

printf( "\n\nThe value of a is %d"
"\nThe value of *aPtr is %d", a, *aPtr );
printf( "\n\nShowing that * and & are complements of "
"each other\n&*aPtr = %p"
"\n*&aPtr = %p\n", &*aPtr *&aPtr  );
return 0;
}

Output :

The address of a is 0012FF7C

The value of aPtr is 0012FF7C

The value of a is 7

The value of *aPtr is 7

Showing that * and & are complements of each other.

&*aPtr = 0012FF7C

*&aPtr = 0012FF7C