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    C++
     
    Bibliothque d'utilitaires
     
    std::hash
     
    <tbody> </tbody>
    Dclar dans l'en-tte <functional>
    template< class Key > struct hash; // not defined
    		 (depuis C++11)
    Le modle de hachage dfinit un objet qui implmente une fonction fonction de hachage. Instances de cet objet de dfinir une fonction operator() que:
    Original:
    The hash template defines a function object that implements a fonction de hachage. Instances of this function object define an operator() that:
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    1. Accepte un seul paramtre de type .. Key
    Original:
    1. Accepts a single parameter of type Key.
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    2. Renvoie une valeur de size_t type qui reprsente la valeur de hachage du paramtre .
    Original:
    2. Returns a value of type size_t that represents the hash value of the parameter.
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    3. Ne pas lever des exceptions en cas d'appel .
    Original:
    3. Does not throw exceptions when called.
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    4. Pour deux paramtres k1 et k2 qui sont gaux, std::hash<Key>()(k1) == std::hash<Key>()(k2) .
    Original:
    4. For two parameters k1 and k2 that are equal, std::hash<Key>()(k1) == std::hash<Key>()(k2).
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    5. Pour deux paramtres diffrents k1 et k2 qui ne sont pas gales, la probabilit que std::hash<Key>()(k1) == std::hash<Key>()(k2) devrait tre trs faible, se rapprochant 1.0/std::numeric_limits<size_t>::max() .
    Original:
    5. 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().
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    Le modle de hachage est la fois CopyConstructible et Destructible .
    Original:
    The hash template is both CopyConstructible and Destructible.
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    Le non-ordonne des conteneurs associatifs std::unordered_set, std::unordered_multiset, std::unordered_map, std::unordered_multimap utiliser spcialisations de la std::hash modle que la fonction de hachage par dfaut .
    Original:
    The unordered associative containers std::unordered_set, std::unordered_multiset, std::unordered_map, std::unordered_multimap use specializations of the template std::hash as the default hash function.
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    Types de membres

    argument_type Key
    result_type std::size_t

    Fonctions membres
    construit un objet fonction de hachage
    Original:
    constructs a hash function object
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    (fonction membre publique)
    calculer l'empreinte de l'argument
    Original:
    calculate the hash of the argument
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    (fonction membre publique)

    Spcialisations standard pour les types de base

    <tbody> </tbody>
    Dclar dans l'en-tte <functional>
    template<> struct hash<bool>; template<> struct hash<char>; template<> struct hash<signed char>; template<> struct hash<unsigned char>; template<> struct hash<char16_t>; template<> struct hash<char32_t>; template<> struct hash<wchar_t>; template<> struct hash<short>; template<> struct hash<unsigned short>; template<> struct hash<int>; template<> struct hash<unsigned int>; template<> struct hash<long>; template<> struct hash<long long>; template<> struct hash<unsigned long>; template<> struct hash<unsigned long long>; template<> struct hash<float>; template<> struct hash<double>; template<> struct hash<long double>; template< class T > struct hash<T*>;

    Spcialisations standard pour les types de bibliothques

    (C++11)
    (C++11)
    (C++11)
    (C++11)
    soutien de hachage pour chaines de caractres
    Original:
    hash support for strings
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    (classe gnrique spcialise) [edit]
    (C++11)
    soutien de hachage pour std::error_code
    Original:
    hash support for std::error_code
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    (classe gnrique spcialise) [edit]
    (C++11)
    soutien de hachage pour std::bitset
    Original:
    hash support for std::bitset
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    (classe gnrique spcialise) [edit]
    (C++11)
    soutien de hachage pour std::unique_ptr
    Original:
    hash support for std::unique_ptr
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    (classe gnrique spcialise) [edit]
    (C++11)
    		 Support du hachage pour std::shared_ptr
    (classe gnrique spcialise) [edit]
    (C++11)
    soutien de hachage pour std::type_index
    Original:
    hash support for std::type_index
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    (classe gnrique spcialise) [edit]
    (C++11)
    soutien de hachage pour std::vector<bool>
    Original:
    hash support for std::vector<bool>
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    (classe gnrique spcialise)
    (C++11)
    soutien de hachage pour std::thread::id
    Original:
    hash support for std::thread::id
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    (classe gnrique spcialise)

    Exemples

    Dmontre le calcul de hachage pour un std::string, un type qui a dj une spcialisation de hachage .

    Original:

    Demonstrates the computation of a hash for std::string, a type that already has a hash specialization.

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    #include <iostream>
#include <functional>
#include <string>

int main()
{
    std::string str = "Meet the new boss...";
    std::hash<std::string> hash_fn;
    size_t str_hash = hash_fn(str);

    std::cout << str_hash << '\n';
}

    Rsultat : 

    391070135

    Dmontre cration d'une fonction de hachage pour un type dfini par l'utilisateur. L'utilisation de ce paramtre comme un modle pour std::unordered_map, std::unordered_set, etc exige galement la spcialisation des std::equal_to .

    Original:

    Demonstrates creation of a hash function for a user defined type. Using this as a template parameter for std::unordered_map, std::unordered_set, etc. also requires specialization of std::equal_to.

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    #include <iostream>
#include <functional>
#include <string>

struct S {
    std::string first_name;
    std::string last_name;
};

template<class T> class MyHash;

template<>
class MyHash<S> {
public:
    size_t operator()(const S &s) const 
    {
        size_t h1 = std::hash<std::string>()(s.first_name);
        size_t h2 = std::hash<std::string>()(s.last_name);
        return h1 ^ (h2 << 1);
    }
};

int main()
{
    std::string s1 = "Hubert";
    std::string s2 = "Farnsworth";
    std::hash<std::string> h1;

    S n1;
    n1.first_name = s1;
    n1.last_name =  s2;

    std::cout << "hash(s1) = " << h1(s1) << "\n"
              << "hash(s2) = " << std::hash<std::string>()(s2) << "\n"
	      << "hash(n1) = " << MyHash<S>()(n1) << "\n";
  
}

    Rsultat : 

    hash(s1) = 6119893563398376542
hash(s2) = 14988020022735710972
hash(n1) = 17649170831080298918

    Montre comment se spcialiser std::hash pour un type dfini par l'utilisateur .

    Original:

    Demonstrates how to specialize std::hash for a user defined type.

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    #include <iostream>
#include <functional>
#include <string>

struct S {
    std::string first_name;
    std::string last_name;
};

namespace std {
template<>
class hash<S> {
public:
    size_t operator()(const S &s) const 
    {
        size_t h1 = std::hash<std::string>()(s.first_name);
        size_t h2 = std::hash<std::string>()(s.last_name);
        return h1 ^ ( h2 << 1 );
    }
};
}

int main()
{
    S s;
    s.first_name = "Bender";
    s.last_name =  "Rodriguez";
    std::hash<S> hash_fn;

    std::cout << "hash(s) = " << hash_fn(s) << "\n";
}

    Rsultat : 

    hash(s) = 32902390710
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