Pointer to Pointer in C

Pointer to Pointer in C

As we know that, a pointer is used to store the address of a variable in C. Pointer reduces the access time of a variable. However, In C, we can also define a pointer to store the address of another pointer. Such pointer is known as a double pointer (pointer to pointer). The first pointer is used to store the address of a variable whereas the second pointer is used to store the address of the first pointer. Let’s understand it by the diagram given below.

int **p;

C double Pointer Example

#include<stdio.h>  
void main ()  
{  
    int a = 10;  
    int *p;  
    int **pp;   
    p = &a; // pointer p is pointing to the address of a  
    pp = &p; // pointer pp is a double pointer pointing to the address of pointer p  
    printf("address of a: %x\n",p); // Address of a will be printed   
    printf("address of p: %x\n",pp); // Address of p will be printed  
    printf("value stored at p: %d\n",*p); // value stoted at the address contained by p i.e. 10 will be printed  
    printf("value stored at pp: %d\n",**pp); // value stored at the address contained by the pointer stoyred at pp  
}  

Output

address of a: d26a8734
address of p: d26a8738
value stored at p: 10
value stored at pp: 10

C double Pointer Example

#include<stdio.h>  
int main(){  
int number=50;      
int *p;//pointer to int    
int **p2;//pointer to pointer        
p=&number;//stores the address of number variable      
p2=&p;    
printf("Address of number variable is %x \n",&number);      
printf("Address of p variable is %x \n",p);      
printf("Value of *p variable is %d \n",*p);      
printf("Address of p2 variable is %x \n",p2);      
printf("Value of **p2 variable is %d \n",*p);      
return 0;  
}  

Output

Address of number variable is fff4
Address of p variable is fff4
Value of *p variable is 50
Address of p2 variable is fff2
Value of **p variable is 50

What is use of double pointer?

We already know that a pointer points to a location in memory and thus used to store address of variables. … The first pointer is used to store the address of second pointer. That is why they are also known as double pointers.

What is pointer to pointer in C with example?

pointer is a variable that stores the address of another variable. Unlike other variables that hold values of a certain type, pointer holds the address of a variable. For example, an integer variable holds (or you can say stores) an integer value, however an integer pointer holds the address of a integer variable.