In C++, delete operator should only be used either for the pointers pointing to the memory allocated using new operator or for a NULL pointer, and free() should only be used either for the pointers pointing to the memory allocated using malloc() or for a NULL pointer.

The most important reason why free() should not be used for de-allocating memory allocated using NEW is that, it does not call the destructor of that object while delete operator does.

CPP

#include<stdio.h>
#include<stdlib.h>
int main()
{
int x;
int *ptr1 = &x;
int *ptr2 = (int *)malloc(sizeof(int));
int *ptr3 = new int;
int *ptr4 = NULL;

/* delete Should NOT be used like below because x is allocated
on stack frame */
delete ptr1;

/* delete Should NOT be used like below because x is allocated
using malloc() */
delete ptr2;

/* Correct uses of delete */
delete ptr3;
delete ptr4;

getchar();
return 0;
}