Introduction to C-Programming As seen in ENGS 20

Recall that memory reserved dynamically via malloc() is completely your responsibility. Therefore, when you are done using the memory it is your job to tell the computer that you no longer need it and thus make available this memory for other purposes. The process of releasing memory is called freeing and we will now learn how to release, or free, memory that has been reserved via malloc() in the heap. The function to do so is called free() and it takes as an argument a pointer to the memory block that you’d like to release.

The prototype for free() is

void free(void *ptr);

The free() function also is a part of the standard library <stdlib.h> and you therefore need to

#include <stdlib.h>

(which you probably already did for the use of malloc().) The following video demonstrates the use of the free() function.

#include <stdio.h>
#include <stdlib.h>
int main(void) {
  int *a, *b;
  float *c;
  a = (int *) malloc(sizeof(int));
  *a = 1;
  b = (int *) malloc(sizeof(int));
  *b = 2;
  free(a);
  free(b);
  c = (float *) malloc(sizeof(float));
  *c = 3.5;
  free(c);
  return 0;
}

printf("a = %d, b = %d, c = %f\n", *a, *b, *c);