NAME¶

std::hash,std::hash,std::hash, - std::hash,std::hash,std::hash,

Synopsis¶

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 of std::hash for the various view classes for hashing
views.

These hashes equal the hashes of corresponding std::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, then std::hash<S>()(s) == std::hash<SV>()(SV(s)).

Example¶

// Run this code

#include <iostream>
#include <string_view>
#include <unordered_set>
using namespace 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_view const& s : stars)
std::cout << s << ' ';
std::cout << '\n';
}

Possible output:¶

"A" #: 6919333181322027406
L"B" #: 11959850520494268278
u8"C" #: 12432341034569643010
u"D" #: 312659256970442235
U"E" #: 18073225910249204957
Arcturus Vega Capella Rigel

See also¶

hash hash function object
(C++11) (class template)

std::hash<std::basic_string> hash support for strings
(C++11) (class template specialization)