The template specializations of std::hash for the various string classes allow users to obtain hashes of strings.

These hashes equal the hashes of corresponding std::basic_string_view classes: If S is one of these 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 ) ) . (since C++17)

[ edit ] Example

#include <functional>
#include <iostream>
#include <memory_resource>
#include <string>
#include <string_view>
using namespace std::literals;
int main()
    auto sv = "Stand back! I've got jimmies!"sv;
    std::string s(sv);
    std::pmr::string pmrs(sv); // use default allocator
    std::cout << std::hash<std::string_view>{}(sv) << '\n';
    std::cout << std::hash<std::string>{}(s) << '\n';
    std::cout << std::hash<std::pmr::string>{}(pmrs) << '\n';
Possible output:
3544599705012401047
3544599705012401047
3544599705012401047
 
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
Applied to
Behavior as published
Correct behavior
LWG 3705
C++11
hash support for std::basic_string with customized allocators was not enabled
enabled
[edit] See also
  
 hash
(C++11)
  hash function object 
 (class template) [edit]
  
 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>
(C++17)(C++17)(C++20)(C++17)(C++17)
  hash support for string views 
 (class template specialization) [edit]
            
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