Pointer to Pointer in C

January 18, 2023

Pointer to Pointer :

Pointer to Pointer in C is defined when the address of the variable is kept in the first pointer. Additionally, the address of the first pointer is kept in the second pointer.

It is also known as double pointers.

Syntax :

Data_Type **  variable_name

Representation of Pointer to Pointer :

Uses of Pointer to Pointer in C :

We can easily accesss 2-D array in C using double pointer.
Command line argument in C
Double pointer can also be used in dynamic memory allocation.

Pointers in C

Pointer to arithmetic in C

Null pointer

Function pointer

Pointer v/s array

Example 1 :

Run

    #include<stdio.h>
    int main()
    {
        int val = 20;
        int *ptr_1;
        int ** ptr_2;    // declaration of double pointer
        ptr_1 = &val;
        ptr_2 = &ptr_1;
        
        //printing the value of different location
        printf("address of val %p\n", ptr_1);
        printf("address of ptr_1: %p\n", ptr_2);
        printf("value stored at ptr_1: %d\n", *ptr_1);
        printf("value stored at ptr_2: %d\n", **ptr_2);
        return 0;
    }

Output :

address of val 0x7ffe67b386e4
address of ptr_1: 0x7ffe67b386e8
value stored at ptr_1: 20
value stored at ptr_2: 20

What Happened Above? Double pointer ptr_2 will print value stored at the address contained by the pointer stored at ptr_2

Example 2

Run

#include<stdio.h>

int main()
{
	int val = 20;
	int* ptr_1 = &val;
	int** ptr_2 = &ptr_1;   // declaration of double pointer


	printf(" Output of program : %d \n", sizeof(ptr_2));
	return 0;
}

Output :

Output of program : 8

What Happened Above? This program will print the size of double pointer in the memory since, we used the sizeof operator in the printf function.

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Pointer to Pointer in C