std::hash

 

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Os operadores relacionais 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 e 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.

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Troque, avançar e avançar 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.

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std::hash

hash::hash

hash::operator()

 

Definido no cabeçalho <functional>
template<class Key > struct hash;// not defined		(desde C++11)

O modelo de hash define um objeto de função que implementa um função hash. Instâncias deste objeto de função definir um operator() que:

Original:

The hash template defines a function object that implements a função hash. Instances of this function object define an operator() that:

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1. Aceita um único parâmetro do tipo Key.

Original:

1. Accepts a single parameter of type Key.

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2. Retorna um valor de size_t tipo que representa o valor de hash do parâmetro.

Original:

2. Returns a value of type size_t that represents the hash value of the parameter.

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3. Não lançar exceções ao chamado.

Original:

3. Does not throw exceptions when called.

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4. Para dois parâmetros k1 e k2 que são iguais, 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. Para dois parâmetros diferentes k1 e k2 que não são iguais, a probabilidade de que std::hash<Key>()(k1)== std::hash<Key>()(k2) deve ser muito pequeno, aproximando-se 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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O modelo de hash é tanto CopyConstructible e Destructible.

Original:

The hash template is both CopyConstructible and Destructible.

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O desordenada contêineres associativos std::unordered_set, std::unordered_multiset, std::unordered_map, std::unordered_multimap usar especializações da std::hash modelo como a função hash padrão.

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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Tipos de membro

argument_type	Key
result_type	std::size_t

Funções de membro

(constructor)	constrói um objeto de função hash Original: constructs a hash function object The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (função pública membro)
operator()	calcular o hash do argumento Original: calculate the hash of the argument The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (função pública membro)

Especializações padrão para tipos básicos

Definido no cabeçalho <functional>
template<>struct hash<bool>; template<>struct hash<char>; template<>struct hash<signedchar>; template<>struct hash<unsignedchar>; template<>struct hash<char16_t>; template<>struct hash<char32_t>; template<>struct hash<wchar_t>; template<>struct hash<short>; template<>struct hash<unsignedshort>; template<>struct hash<int>; template<>struct hash<unsignedint>; template<>struct hash<long>; template<>struct hash<longlong>; template<>struct hash<unsignedlong>; template<>struct hash<unsignedlonglong>; template<>struct hash<float>; template<>struct hash<double>; template<>struct hash<longdouble>; template<class T >struct hash<T*>;

Especializações padrão para tipos de biblioteca

std::hash<std::string> std::hash<std::u16string> std::hash<std::u32string> std::hash<std::wstring> (C++11) (C++11) (C++11) (C++11)	apoio de hash para strings Original: hash support for strings The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (especialização modelo. classe)
std::hash<std::error_code> (C++11)	apoio de hash para std::error_code Original: hash support for std::error_code The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (especialização modelo. classe)
std::hash<std::bitset> (C++11)	apoio de hash para std::bitset Original: hash support for std::bitset The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (especialização modelo. classe)
std::hash<std::unique_ptr> (C++11)	apoio de hash para std::unique_ptr Original: hash support for std::unique_ptr The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (especialização modelo. classe)
std::hash<std::shared_ptr> (C++11)	apoio de hash para std::shared_ptr Original: hash support for std::shared_ptr The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (especialização modelo. classe)
std::hash<std::type_index> (C++11)	apoio de hash para std::type_index Original: hash support for std::type_index The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (especialização modelo. classe)
std::hash<std::vector<bool>> (C++11)	apoio de hash para std::vector<bool> Original: hash support for std::vector<bool> The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (especialização modelo. classe)
std::hash<std::thread::id> (C++11)	apoio de hash para std::thread::id Original: hash support for std::thread::id The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (especialização modelo. classe)

Exemplos

Demonstra o cálculo de um hash para std::string, um tipo que já tem uma especialização de hash .

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';}

Saída:

391070135

Demonstra a criação de uma função hash para um tipo definido pelo usuário. Usando isso como um parâmetro de modelo para std::unordered_map, std::unordered_set, etc também exige especialização de 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";   }

Saída:

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

Demonstra como se especializar std::hash para um tipo definido pelo usuário .

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";}

Saída:

hash(s) = 32902390710