According to the C language spec, casting from integer to pointers is implementation defined. Though one would expect it to work, the spec does not require compilers to allow it.

For example, for accessing VGA text video memory, one would write (in D):

byte *video = cast(byte *)0xB8000;

As a systems' programming language, existing D compilers surely do allow that. But does the spec actually require it, or simply allow it?