C Pointer to pointer
A pointer to a pointer is a form of multiple indirection, or a chain of pointers. Normally, a pointer contains the address of a variable. When we define a pointer to a pointer, the first pointer contains the address of the second pointer, and the second pointer points to the location that contains the actual value.
A pointer to a pointer variable must be declared as follows, placing two asterisks before the variable name. For example, the following declares a pointer to an int pointer:
int **var;
When a target value is indirectly pointed to by a pointer to another pointer, accessing this value requires the use of two asterisk operators, as shown in the following example:
Example
#include <stdio.h>
int main ()
{
int V;
int *Pt1;
int **Pt2;
V = 100;
/*Get the address of V*/
Pt1 = &V;
/*Use the & operator to get the address of Pt1*/
Pt2 = &Pt1;
/*Use pptr to get the value*/
printf("var = %d\n", V );
printf("Pt1 = %p\n", Pt1 );
printf("*Pt1 = %d\n", *Pt1 );
printf("Pt2 = %p\n", Pt2 );
printf("**Pt2 = %d\n", **Pt2);
return 0;
}
When the above code is compiled and executed, it produces the following results:
var = 100 Pt1 = 0x7ffee2d5e8d8 *Pt1 = 100 Pt2 = 0x7ffee2d5e8d0 **Pt2 = 100other extensions