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Difference between revisions of "cpp/string/basic string/hash"

From cppreference.com
< cpp‎ | string‎ | basic string
m (fix u8tring to u8string)
m (→‎Example: shorten and use the result from libstdc++)
Line 38: Line 38:
 
{
 
{
 
     std::string s = "Stand back! I've got jimmies!";
 
     std::string s = "Stand back! I've got jimmies!";
−
     std::hash<std::string> hash_fn;
+
−
 
+
     std::cout << std::hash<std::string>{}(s) << '\n';
−
    size_t hash = hash_fn(s);
+
−
 
+
−
    std::cout << hash << '\n';
+
 
}
 
}
 +
| p=true
 
  | output=
 
  | output=
−
325378910
+
3544599705012401047
 
}}
 
}}
  

Revision as of 20:37, 18 August 2019

 
C++
 
Strings library
 
std::basic_string
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hash<std::basic_string>
(C++11)
Deduction guides (C++17)

 
Defined in header <string>
template<> struct hash<std::string>;

template<> struct hash<std::wstring>;
template<> struct hash<std::u8string>; // c++20
template<> struct hash<std::u16string>;

template<> struct hash<std::u32string>;
 (since C++11)
template<> struct hash<std::pmr::string>;

template<> struct hash<std::pmr::wstring>;
template<> struct hash<std::pmr::u8string>;
template<> struct hash<std::pmr::u16string>;

template<> struct hash<std::pmr::u32string>;
 (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 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)

Example

The following code shows one possible output of a hash function used on a string:

Run this code
#include <iostream>
#include <string>
#include <functional>
 
int main()
{
    std::string s = "Stand back! I've got jimmies!";
 
    std::cout << std::hash<std::string>{}(s) << '\n';
}

Possible output: 

3544599705012401047

See also

(C++11)
 hash function object
(class template) [edit]
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