[joosteto]

When I compile the example, i get:

  0x7ffd0b57ebd0 0x7ffd0b57ebd8 0

OK, so gcc reordered a & b; I'll fix this by chaning the initialisation of p and q to:

  int *p = &a + 1;
  int *q = &b;

But when I now run the example, I get:

  gcc -o c c.c && ./c
  0x7ffe55eb0aa4 0x7ffe55eb0aa4 1

  gcc -O -o c c.c && ./c
  0x7ffcfeffd914 0x7ffcfeffd914 0

So, p==q only evaluates to 1 if optimisation is enabled.

  $ gcc --version
  gcc (Ubuntu 7.3.0-16ubuntu3) 7.3.0

[psyklic]

It shows the exact options the author used if you click on GCC:

Version: 8.1.1 Options: -std=c11 -O1 Target: x86_64-redhat-linux