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* [Bug libstdc++/99752] New: ranges::find_end should return empty subrange when search range is empty @ 2021-03-24 14:19 hewillk at gmail dot com 2021-03-24 14:48 ` [Bug libstdc++/99752] " hewillk at gmail dot com ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: hewillk at gmail dot com @ 2021-03-24 14:19 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99752 Bug ID: 99752 Summary: ranges::find_end should return empty subrange when search range is empty Product: gcc Version: 11.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: libstdc++ Assignee: unassigned at gcc dot gnu.org Reporter: hewillk at gmail dot com Target Milestone: --- In ranges::find_end implementation: 674 else 675 { 676 auto __i = ranges::next(__first1, __last1); 677 if (__first2 == __last2) 678 return {__i, __i}; when the examined range is not bidirectional_range and the search range is empty, we still do the ranges::next call, this makes the following code infinite loop: #include <algorithm> #include <ranges> int main() { auto r = std::views::iota(0); std::ranges::empty_view<int> e; std::ranges::find_end(r, e); } But according to the [alg.find.end]: "i be last1 if [first2, last2) is empty", so I think this is a library bug since in such case ranges::find_end never return. Same situations in ranges::rotate with performance loss in more rare conditions: 1573 { 1574 auto __lasti = ranges::next(__first, __last); 1575 if (__first == __middle) 1576 return {__lasti, __lasti}; 1577 if (__last == __middle) 1578 return {std::move(__first), std::move(__lasti)}; ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug libstdc++/99752] ranges::find_end should return empty subrange when search range is empty 2021-03-24 14:19 [Bug libstdc++/99752] New: ranges::find_end should return empty subrange when search range is empty hewillk at gmail dot com @ 2021-03-24 14:48 ` hewillk at gmail dot com 2021-03-24 14:53 ` hewillk at gmail dot com 2021-03-24 14:56 ` redi at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: hewillk at gmail dot com @ 2021-03-24 14:48 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99752 --- Comment #1 from 康桓瑋 <hewillk at gmail dot com> --- My pardon, since the ranges::find_end return type is ranges::subrange<I1>, we still to get the common last1 iterator through the ranges::next call, so this seems not a bug. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug libstdc++/99752] ranges::find_end should return empty subrange when search range is empty 2021-03-24 14:19 [Bug libstdc++/99752] New: ranges::find_end should return empty subrange when search range is empty hewillk at gmail dot com 2021-03-24 14:48 ` [Bug libstdc++/99752] " hewillk at gmail dot com @ 2021-03-24 14:53 ` hewillk at gmail dot com 2021-03-24 14:56 ` redi at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: hewillk at gmail dot com @ 2021-03-24 14:53 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99752 康桓瑋 <hewillk at gmail dot com> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |INVALID --- Comment #2 from 康桓瑋 <hewillk at gmail dot com> --- Since the ranges::find_end return type is ranges::subrange<I1>, we still to get the common last1 iterator through the ranges::next call, so this seems not a bug. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug libstdc++/99752] ranges::find_end should return empty subrange when search range is empty 2021-03-24 14:19 [Bug libstdc++/99752] New: ranges::find_end should return empty subrange when search range is empty hewillk at gmail dot com 2021-03-24 14:48 ` [Bug libstdc++/99752] " hewillk at gmail dot com 2021-03-24 14:53 ` hewillk at gmail dot com @ 2021-03-24 14:56 ` redi at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: redi at gcc dot gnu.org @ 2021-03-24 14:56 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99752 --- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> --- Your example is an infinite loop because you're asking for the last occurrence of e in an infinite range. There is no end of an infinite range. ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-03-24 14:56 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-03-24 14:19 [Bug libstdc++/99752] New: ranges::find_end should return empty subrange when search range is empty hewillk at gmail dot com 2021-03-24 14:48 ` [Bug libstdc++/99752] " hewillk at gmail dot com 2021-03-24 14:53 ` hewillk at gmail dot com 2021-03-24 14:56 ` redi at gcc dot gnu.org
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