Question

Here is my program:

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

main(){
   char *p1, *p2, *p3, *p4;

   p1 = (char*)malloc(10);
   p2 = (char*)malloc(10);
   p3 = (char*)malloc(16);
   p4 = (char*)malloc(32);

   printf("p1 points at: %d\n", p1);
   printf("p2 points at: %d\n", p2);
   printf("p3 points at: %d\n", p3);
   printf("p4 points at: %d\n\n", p4);

   system("PAUSE");
}

This produces the following output on my PC:

p1 points at: 6492080

p2 points at: 6492104

p3 points at: 6492128

p4 points at: 6492152

So, each memory space that malloc allocates starts 24 bytes further, no matter how many bytes are allocated. Why is that? I appreciate your help!

Answer 1

malloc shall allocate space for an object of size size. Nothing prevents your implementation to add padding bytes for alignment purpose, for instance. Another example: some memory management implementations keep the size of your block before the allocated space.

If you want more details, you should precise your implementation.