You're technically right, because you can have C compilers for architectures with all sorts of weird memory semantics. But in reality, this will work as expecte

You're technically right, because you can have C compilers for architectures with all sorts of weird memory semantics. But in reality, this will work as expected on all of the major platforms and give you the relative positions of the variables on the stack. The C standard is not the final say on things, your compiler and platform are. The standard is merely the minimum specifications that are ideally to be supported on all platforms, however you will still be unpleasantly surprised if you rely on it as such.