Question

What is the use of a double pointer (pointer to pointer) in C?

Answer 1

There is a lot of application of double-pointer in C language but here I am describing one important application of double-pointer. If you want to create a function to allocate the memory and you want to get back the allocated memory from the function parameter, then you need to use the double-pointer in that scenario. See the below code,

#include<stdio.h>

#include<stdlib.h>

void AllocateMemory(int **pGetMemory,int n)

{

int *p = malloc(sizeof(int)*n);

if(p == NULL)

{

*pGetMemory = NULL;

}

else

{

*pGetMemory = p;

}

}

int main()

{

int *arr = NULL;

int len = 10;

int i =0;

//Allocate the memory

AllocateMemory(&arr,len);

if(arr == NULL)

{

printf("Failed to allocate the memory\n");

return -1;

}

//Store the value

for(i=0; i<len; i++)

{

arr[i] = i;

}

//print the value

for(i=0; i<len; i++)

{

printf("arr[%d] = %d\n",i, arr[i]);

}

//free the memory

free(arr);

return 0;

}

Output: