heap_example.c

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

int main(int argc, char *argv[]) {
    char *char_ptr;
    int *int_ptr;
    int mem_size;
    
    if(argc<2)
        mem_size = 50;
    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);
    
    if(char_ptr == NULL){
        fprintf(stderr, "Error: could not allocate heap memory.\n");
        exit(-1);
    }
    
    strcpy(char_ptr, "This is memory location 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);
    
    if(int_ptr == NULL) {
        fprintf(stderr, "Error: could not allocate heap memory.\n");
        exit(-1);
    }
    
    *int_ptr = 31337;
    printf("int_ptr (%p) --> %d\n", int_ptr, *int_ptr);
    
    printf("\t[-] freeing char_ptr's heap memory...\n");
    free(char_ptr);
    
    printf("\t[+] allocating another 15 bytes for char_ptr\n");
    char_ptr = (char *) malloc(15);
    
    if(char_ptr == NULL) {
        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);
    printf("\t[-] freeing char_ptr's heap memory...\n");
    free(char_ptr);
}

/*
Output:
[+] allocating 50 bytes of memory on the heap for char_ptr
char_ptr (0x55d2003b76b0) --> 'This is memory location on the heap'
	[+] allocating 12 bytes of memory on the heap for int_ptr
int_ptr (0x55d2003b76f0) --> 31337
	[-] freeing char_ptr's heap memory...
	[+] allocating another 15 bytes for char_ptr
char_ptr (0x55d2003b7710) --> 'new memory'
	[-] freeing int_ptr's heap memory...
	[-] freeing char_ptr's heap memory...
*/