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std::hash<std::string_view>, std::hash<std::wstring_view>, std::hash<std::u8string_view>, std::hash<std::u16string_view>, std::hash<std::u32string_view>

From cppreference.com
 
C++
 
Strings library
 
std::basic_string_view
 
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)).

[edit] 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

[edit] See also

(C++11)
 hash function object
(class template) [edit]
(C++11)
 hash support for strings
(class template specialization) [edit]
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