Question

Working my way through a C tutorial

#include <stdio.h>

int main() {
  short s = 10;
  int i = *(int *)&s; // wonder about this
  printf("%i", i);
  return 0;
}

When I tell C that the address of s is an int, should it not read 4 bytes?

Starting from the left most side of 2 bytes of s. In which case is this not critically dangerous as I don’t know what it is reading since the short only assigned 2 bytes?

Should this not crash for trying to access memory that I haven’t assigned/belong-to-me?

Answer 1

First of all, never do this.

As to why it doesn’t crash: since s is a local, it’s allocated on the stack. If short and int have different sizes in your architecture (which is not a given), then you will probably end up reading a few more bytes from memory that’s on the same memory page as the stack; so and there will be no access violation (even though you will read garbage).

Probably.