Operators on Pointers

• & "address of"
• * "contents of" or de-reference or "value pointed to by"

Example

int x, y;
int *p1, *p2;  /* Declare 2 pointers to int,   */
               /* p1 and p2                    */

x = -42;
y = 163;

p1 = &x;       /* p1 holds the address of x    */   
p2 = &y;       /* p2 holds the address of y    */   

*p1 = 17;      /* Put the value 17 into the    */
               /* container that p1 points to  */

p1 = p2;       /* Let the variable p1 now hold */ 
	       /* the same address as p2 holds */

p1 = &x;       /* p1 holds the address of x    */
   
*p1 = *p2;     /* Put the value found at the   */
               /* address that p2 points to    */
	       /* into the container that p1   */
	       /* points to.                   */

NULL

NULL is usually represented by 0 -- the address of the first byte in memory.

Since most C compilers do not put in code to check that your program is not trying to access the contents of the null pointer, you can generate tricky bugs by doing so.