free with NULL clear to avoid double-free

free_with_null.c

#include <stdio.h>
#include <stdlib.h>

// free and set NULL
// need to specify address of pointer of allocated memory block
void free_with_null(void **ptr)
{
  free(*ptr);
	*ptr = NULL;
}

int main(void)
{
	int *mem = malloc(sizeof(int) * 10);
	printf("mem=%p -> ", mem);
  // normal free
	free(mem);
	printf("free -> mem=%p\n", mem);
	
	mem = malloc(sizeof(int) * 10);
	printf("mem=%p -> ", mem);
  // free with NULL
	free_with_null(&mem);
	printf("free -> mem=%p\n", mem);

	return 0;
}