memcmp() and sizeof()

main.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdbool.h>

struct Foo
{
  int i;
  char j;
};

void trash(size_t size)
{
  int fd = open("/dev/random", O_RDONLY);
  char* buffer = (char*)malloc(size);
  read(fd, buffer, size);
  free(buffer);
  close(fd);
}

int main(int argc, char* argv[])
{
  printf("sizeof(struct Foo): %d\n", (int)sizeof(struct Foo));

  bool fail = false;
  for (;!fail;)
  {
    trash(10000);
    struct Foo* foo1 = (struct Foo*)malloc(sizeof(struct Foo));
    trash(10000);
    struct Foo* foo2 = (struct Foo*)malloc(sizeof(struct Foo));

    foo1->i = foo2->i = 1;
    foo1->j = foo2->j = 2;

    if (memcmp(foo1, foo2, sizeof(struct Foo)) == 0)
    {
      printf(".");
    }
    else
    {
      printf("X\n");
      fail = true;
    }

    free(foo1);
    free(foo2);
  }

  return 0;
}