On Mon, 20 Aug 2018 at 09:27, Richard Biener <richard.guent...@gmail.com> wrote: > > On Wed, Aug 15, 2018 at 7:44 AM Liu Hao <lh_mo...@126.com> wrote: > > > > 在 2018-08-15 12:48, Jeff Law 写道: > > > I just don't think anyone's ever bothered to catch this case. I believe > > > there is a BZ which touches on this issue. > > > > > > > Yes, here it is: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78655 > > > > This PR uses a placement new as the example, which in GCC 8 assumes the > > pointer argument to `operator new()` is never null. But for a general > > case it is still not fixed. > > > > So it looks like nobody has been working on this. I will just fix my > > code then. > > 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?
C11 6.5.6 paragraph 8 says the result is only defined if the pointer and the result of the addition point to elements of the same array object, or one past the end of the array (where a non-array object is treated as an array of one element as per paragraph 7). Since a null pointer doesn't point to an object, the pointer and the result of the addition do not point to the same array. C++17 has similar wording in 8.7 [expr.add] paragraph 4.
