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Explain the concept of pointer to pointer and void pointer in C language?
Double pointer or pointer to pointer is a variable that holds the address of another pointer.
Following is the declaration for a pointer to a pointer −
datatype ** pointer_name;
For example, int **p; p is a pointer to pointer
Initialization − ‘&’ is used for initialization.
For example,
int a = 10; int *p; int **q; p = &a;
Accessing − Indirection operator (*) is used for accessing.
Example
Following is the C program for the pointer to pointer −
#include<stdio.h>
main ( ){
int A = 10;
int *p;
int **q;
p = &A;
q = &p;
printf("A =%d",A);
printf("A value of pointer = %d", *p);
printf("A value of double pointer = %d", **q);
}Output
When the above program is executed, it produces the following result −
A=10 A value of pointer = 10 A value of double pointer = 10
Void pointers
It is a type of pointer that can hold the address of any datatype variable (or) can point to any datatype variable.
Following is the declaration for the void pointer −
void *pointername;
For example, void *vp;
Accessing − Type cast operator is for accessing the value of a variable through its pointer.
The syntax is as follows −
* ( (type cast) void pointer)
For example,
int i=10;
void *vp;
vp = &i;
printf ("%d", * ((int*) vp));
type castExample
Following is the C program for the void pointer −
#include<stdio.h>
main ( ){
int i =10;
float f = 5.34;
void *vp;
clrscr ( );
vp = &i;
printf ("i = %d", * ((int*)vp));
vp = &f;
printf ( "f = %f", * ((float*) vp));
getch ( );
}Output
When the above program is executed, it produces the following result −
i = 10 f = 5.34
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