Boost C++ Libraries: Ticket #11150: string_ref::to_string is necessarily UB for a default-constructed string_ref, despite stating no preconditions

Marshall Clow — Sat, 28 Mar 2015 18:56:01 GMT

Interestingly enough, this section of the standard [string.cons] has changed over time.

Specifically the bit about this constructor:

basic_string(const charT* s, size_type n, const Allocator& a = Allocator());

C++03 and C++11 have the following requirement: "Requires: s shall not be a null pointer and n < npos"

C++14 says instead: "Requires: s points to an array of at least n elements of charT."

{ NULL, 0 } is allowable in the second case, but not in the first.

status changed; resolution set

Marshall Clow — Sat, 28 Mar 2015 19:07:55 GMT

status new → closed
resolution → fixed

Committed 13610caa36edcae896f59246a2933ef4772690f4 to fix this.

Tomalak Geret'kal — Sat, 28 Mar 2015 23:16:37 GMT

I disagree. There is such a thing as an array of [at least] 0 elements of charT:

char* ptr = new char[0];
delete[] ptr;

and a NULL pointer cannot ever point to such an array. It doesn't point to anything.

Tomalak Geret'kal — Sat, 28 Mar 2015 23:24:32 GMT

Thanks for fixing, anyway. :)

(Please note that, as you can see, I'm having real difficulty with Trac at the moment. Submissions take a good minute and one appeared to fail but then apparently succeeded. And led to two "comment 3"s?!)