Question

How is Pointers subtraction in C?

Answer 1

We can also subtract one pointer from another pointer. This technique is useful when we need to calculate the number of bytes between the two pointers. But pointers subtraction is useful when they are pointing the same array or memory block.

If subtract two pointers that pointing the same array, the result of this subtraction gives the number of elements that separate them. Let’s consider two examples which describe the subtraction of two number.

Example 1:

In this example, we will calculate the size of the structure to subtract the pointers.

 

#include <stdio.h>

#include <stdlib.h>

typedef struct

{

int Age;

float Weight;

} sInfo;

int main()

{

//create an array of structure;

sInfo JhonFamilyInfo[2];

//Create pointer to the structure

sInfo *psInfo = NULL;

int iSizeofStructure = 0;

//Assign the address of array to the pointer

psInfo = JhonFamilyInfo;

// Subtract the pointer

iSizeofStructure = (char*)(psInfo + 1) - (char*)(psInfo);

printf("Size of structure = %d\n\n",iSizeofStructure);

return 0;

}

Output: Size of structure =  8