在 2018-08-20 16:27, Richard Biener 写道: > Btw, I can't find wording in the standards that nullptr + 1 is > invoking undefined behavior, > that is, that pointer arithmetic is only allowed on pointers pointing > to a valid object. > Any specific pointers? >
The C standard only defines addition and subtraction for pointers pointing to elements and past-the-end positions of arrays [1]. As a null pointer ipoints to nothing, the 'otherwise' clauses apply, rendering the behavior undefined. The C++ standard has a couple of similar paragraphs [2]. In addition to that, there is a special case for null pointers and the integer zero [3]. There is no special case for null pointers and integers other than zero. [1] ISO/IEC WG14 N1570, 6.5.6 Additive operators, 8, 9. [2] ISO/IEC WG21 N4750, 8.5.6 Additive operators, 4, 5 [3] ISO/IEC WG21 N4750, 8.5.6 Additive operators, 7 -- Best regards, LH_Mouse
