Arithmetic on function address

[Richard Bos]

Note that conversion of integer constant to a pointer is explicitly
defined to result in an address constant - and according to 6.3.2.3.5
it may not cause undefined behavior.

Actually, in a practical sense it may, unless the value is immediately
discarded (which would make the entire conversion useless). It can
result in incorrectly aligned or trap pointers, any use of which do have
undefined behaviour.

Richard