https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113202
--- Comment #9 from Xi Ruoyao <xry111 at gcc dot gnu.org> --- (In reply to Carsten Schmidt from comment #6) > > Why do you think this is a bug? > > 1. Considering the "possible implementation" of cppreference.com, pointer > arithmetic, e.g. ptr-ptr, should not be an issue when searching for the > sentinel. Quoting from https://en.cppreference.com/w/cpp/iterator: <quote> An iterator j is called reachable from an iterator i if and only if there is a finite sequence of applications of the expression ++i that makes i == j. If j is reachable from i, they refer to elements of the same sequence. A range is a pair of iterators that designate the beginning and end of the computation. A range [i, i) is an empty range; in general, a range [i, j) refers to the elements in the data structure starting with the element pointed to by i and up to but not including the element pointed to by j. Range [i, j) is valid if and only if j is reachable from i. </quote> Here there is no finite sequences of applications of the expression ++i that makes i == j because running ++i will invoke undefined behavior far before i == j. Thus this range is invalid. And: <quote> The result of the application of functions in the standard library to invalid ranges is undefined. </quote>
