Espacios de nombres
Variantes
Acciones

std::hash<Key>::operator()

De cppreference.com
< cpp‎ | utility‎ | hash

 
 
Utilidades de la biblioteca
Escriba apoyo (basic types, RTTI, type traits)
Gestión de memoria dinámica
Gestión de errores
Programa de servicios públicos
Funciones variadic
Fecha y hora
Objetos Function
initializer_list(C++11)
bitset
hash(C++11)
Operadores relacionales
Original:
Relational operators
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=
Pares y tuplas
Original:
Pairs and tuples
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
pair
tuple(C++11)
piecewise_construct_t(C++11)
piecewise_construct(C++11)
Cambiar, hacia adelante y mover
Original:
Swap, forward and move
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
swap
forward(C++11)
move(C++11)
move_if_noexcept(C++11)
declval(C++11)
 
std::hash
hash::hash
hash::operator()
 

Specializations of std::hash should define an operator() that:

  • Takes a single argument key of type Key.
  • Returns a value of type size_t that represents the hash value of key.
  • For two parameters k1 and k2 that are equal, std::hash<Key>()(k1) == std::hash<Key>()(k2).
  • For two different parameters k1 and k2 that are not equal, the probability that std::hash<Key>()(k1) == std::hash<Key>()(k2) should be very small, approaching 1.0/std::numeric_limits<size_t>::max().

Contenido

[editar] Parámetros

key - the object to be hashed

[editar] Valor de retorno

a size_t representing the hash value

[editar] Excepciones

Hash functions should not throw exceptions.

[editar] Ejemplo

The following code shows how to specialize the std::hash template for a custom class.

#include <functional>
#include <iostream>
#include <string>
 
struct Employee {
  std::string name;
  unsigned int ID;
};
 
namespace std {
template <>
class hash<Employee> {
 public:
  size_t operator()(const Employee &employee) const
  {
    // computes the hash of an employee using a variant 
    // of the Fowler-Noll-Vo hash function
    size_t result = 2166136261;
 
    for (size_t i = 0, ie = employee.name.size(); i != ie; ++i) {
      result = (result * 16777619) ^ employee.name[i];
    }
 
    return result ^ (employee.ID << 1);
  }
};
}
 
int main()
{
  Employee employee;
  employee.name = "Zaphod Beeblebrox";
  employee.ID = 42;
 
  std::hash<Employee> hash_fn;
  std::cout << hash_fn(employee) << '\n';
}

Output:

177237019