heap_example.c

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

int main(int argc, char *argv[]) {
   char *char_ptr;  // a char pointer
   int *int_ptr;    // an integer pointer
   int mem_size;

   if (argc < 2)     // if there aren't commandline arguments,
      mem_size = 50; // use 50 as the default value..
   else
      mem_size = atoi(argv[1]);

   printf("\t[+] allocating %d bytes of memory on the heap for char_ptr\n", mem_size);
   char_ptr = (char *) malloc(mem_size); // allocating heap memory

   if(char_ptr == NULL) {  // error checking, in case malloc() fails
      fprintf(stderr, "Error: could not allocate heap memory.\n");
      exit(-1);
   }

   strcpy(char_ptr, "This is memory is located on the heap.");
   printf("char_ptr (%p) --> '%s'\n", char_ptr, char_ptr);

   printf("\t[+] allocating 12 bytes of memory on the heap for int_ptr\n");
   int_ptr = (int *) malloc(12); // allocated heap memory again

   if(int_ptr == NULL) {  // error checking, in case malloc() fails
      fprintf(stderr, "Error: could not allocate heap memory.\n");
      exit(-1);
   }

   *int_ptr = 31337; // put the value of 31337 where int_ptr is pointing
   printf("int_ptr (%p) --> %d\n", int_ptr, *int_ptr);


   printf("\t[-] freeing char_ptr's heap memory...\n");
   free(char_ptr); // freeing heap memory

   printf("\t[+] allocating another 15 bytes for char_ptr\n");
   char_ptr = (char *) malloc(15); // allocating more heap memory

   if(char_ptr == NULL) {  // error checking, in case malloc() fails
      fprintf(stderr, "Error: could not allocate heap memory.\n");
      exit(-1);
   }

   strcpy(char_ptr, "new memory");
   printf("char_ptr (%p) --> '%s'\n", char_ptr, char_ptr);

   printf("\t[-] freeing int_ptr's heap memory...\n");
   free(int_ptr); // freeing heap memory
   printf("\t[-] freeing char_ptr's heap memory...\n");
   free(char_ptr); // freeing the other block of heap memory
}