C | Dynamic Memory Allocation | Question 7

What is the problem with following code?

#include<stdio.h>
int main()
{
    int *p = (int *)malloc(sizeof(int));

    p = NULL;

    free(p);
}

(A) Compiler Error: free can’t be applied on NULL pointer
(B) Memory Leak
(C) Dangling Pointer
(D) The program may crash as free() is called for NULL pointer.


Answer: (B)

Explanation: free() can be called for NULL pointer, so no problem with free function call.

The problem is memory leak, p is allocated some memory which is not freed, but the pointer is assigned as NULL. The correct sequence should be following:

    free(p);
    p = NULL;

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