std::hash<std::basic_string>

Since C++11

Header: <string>

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

# Declarations

template< class A >
struct hash<std::basic_string<char, std::char_traits<char>, A>>;

(since C++11)

template< class A >
struct hash<std::basic_string<char16_t, std::char_traits<char16_t>, A>>;

(since C++11)

template< class A >
struct hash<std::basic_string<char32_t, std::char_traits<char32_t>, A>>;

(since C++11)

template< class A >
struct hash<std::basic_string<wchar_t, std::char_traits<wchar_t>, A>>;

(since C++11)

template< class A >
struct hash<std::basic_string<char8_t, std::char_traits<char8_t>, A>>;

(since C++20)

# 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';
}

# Defect reports

DRApplied toBehavior as publishedCorrect behavior
LWG 3705C++11hash support for std::basic_string with customized allocators was not enabledenabled

# See also