An Example
The Program
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/*********************************************
** File: pointers.c
** Author: R. Chang
** Modified by: S. Evans
** Date: 3/2/04
** Modified to conform to current 201 standards
** Section: 101
** EMail: bogar@cs.umbc.edu
**
** A simple program that shows the addresses of
** variables and that those addresses are stored
** in the pointer variables that point to them.
**********************************************/
#include <stdio.h>
int main ()
{
int a = 1, b = 2;
/* pointer declarations */
int *ptr1, *ptr2 ;
/* show value and address of a and value of the pointer */
ptr1 = &a ;
printf("a = %d, &a = %p, ptr1 = %p, *ptr1 = %d\n",
a, &a, ptr1, *ptr1) ;
/* show value and address of b and value of the pointer */
ptr1 = &b ;
printf("b = %d, &b = %p, ptr1 = %p, *ptr1 = %d\n",
b, &b, ptr1, *ptr1) ;
/* change the value of b by dereferencing the ptr1 */
*ptr1 = 35 ;
printf("b = %d, &b = %p, ptr1 = %p, *ptr1 = %d\n",
b, &b, ptr1, *ptr1) ;
/* let ptr2 also point to b */
ptr2 = ptr1 ;
/* and also change b by dereferencing ptr2 */
*ptr2 = 17 ;
printf("b = %d, &b = %p, ptr1 = %p, *ptr1 = %d\n",
b, &b, ptr1, *ptr1) ;
return 0;
}
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Output
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linux1[75] % gcc -Wall -ansi pointers.c
linux1[76] % a.out
a = 1, &a = 0x7ffffa94, ptr1 = 0x7ffffa94, *ptr1 = 1
b = 2, &b = 0x7ffffa90, ptr1 = 0x7ffffa90, *ptr1 = 2
b = 35, &b = 0x7ffffa90, ptr1 = 0x7ffffa90, *ptr1 = 35
b = 17, &b = 0x7ffffa90, ptr1 = 0x7ffffa90, *ptr1 = 17
linux1[77] %
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