std::hash(std::basic_string)
Defined in header <string>
|
||
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<char8_t, std::char_traits<char8_t>, A>>; |
(since C++20) | |
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 |
(since C++17) |
[edit] Example
The following code shows one possible output of a hash function used on a string:
#include <iostream> #include <string> #include <string_view> #include <functional> #include <memory_resource> 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.
DR | 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
(C++11) |
hash function object (class template) |
hash support for string views (class template specialization) |