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Defined in header <string_view> | ||
template<>struct hash<std::string_view>; | (since C++17) | |
template<>struct hash<std::wstring_view>; | (since C++17) | |
template<>struct hash<std::u8string_view>; | (since C++20) | |
template<>struct hash<std::u16string_view>; | (since C++17) | |
template<>struct hash<std::u32string_view>; | (since C++17) | |
Template specializations ofstd::hash for the various view classes for hashing views.
These hashes equal the hashes of correspondingstd::basic_string classes: If S is one of the standard basic_string types, SV is the corresponding string view type, and s is an object of type S, thenstd::hash<S>()(s)==std::hash<SV>()(SV(s)).
#include <iostream>#include <string_view>#include <unordered_set>usingnamespace std::literals; int main(){std::cout<<"\"A\" #: "<<std::hash<std::string_view>{}("A"sv)<<'\n';std::cout<<"L\"B\" #: "<<std::hash<std::wstring_view>{}(L"B"sv)<<'\n';std::cout<<"u8\"C\" #: "<<std::hash<std::u8string_view>{}(u8"C"sv)<<'\n';std::cout<<"u\"D\" #: "<<std::hash<std::u16string_view>{}(u"D"sv)<<'\n';std::cout<<"U\"E\" #: "<<std::hash<std::u32string_view>{}(U"E"sv)<<'\n'; // std::hash for string_view family makes it possible to keep these view-types// in unordered_* associative containers, such as unordered_set. But ensure// the lifespan of referenced strings is no less than lifespan of the container,// i.e. no dangling references occurred. std::unordered_set stars{"Rigel"sv,"Capella"sv,"Vega"sv,"Arcturus"sv}; for(std::string_viewconst& s: stars)std::cout<< s<<' ';std::cout<<'\n';}
Possible output:
"A" #: 6919333181322027406L"B" #: 11959850520494268278u8"C" #: 12432341034569643010u"D" #: 312659256970442235U"E" #: 18073225910249204957Arcturus Vega Capella Rigel
(C++11) | hash function object (class template)[edit] |
(C++11) | hash support for strings (class template specialization)[edit] |
