Pointers

• A pointer is a variable which holds a memory address --- usually points to another variable.

Declaration:

int *ptr; /* declare a pointer to an integer */ int i,j, *ptr2; /* declare two integers and a pointer to an integer */

• The operator & returns the address of an object:

  int number; ptr = &number; /* address of number assigned to ptr */

  
  
  
• The operator * is used to de-reference a pointer yielding the value of the object pointed at (contents of).

For example:

int number = 7; int number_2; int *ptr; ... ptr = &number; printf("address of number is %x \n",ptr); /* %x : hexadecimal */ printf("ptr points to the value %d \n", *ptr); /* *ptr : de-ref ptr */

may produce

address of number is 0x434560 ptr points to the value 7

and then

number_2 = *ptr + 5; /* set number_2 value 12 */ *ptr = 80; /* set number to 80 */