Namensräume
Varianten
Aktionen

std::hash

Aus cppreference.com
< cpp‎ | utility

This page has been machine-translated from the English version of the wiki using Google Translate.

The translation may contain errors and awkward wording. Hover over text to see the original version. You can help to fix errors and improve the translation. For instructions click here.

Click here for the English version of this page


 
C++
 
Utilities-Bibliothek
 
std::hash
 
definiert in Header <functional>
template< class Key >
struct hash; // not defined
 (seit C++11)
Das Hash-Template definiert ein Funktionsobjekt, das eine Hash-Funktion implementiert. Instanzen dieses Funktionsobjekts definieren einen operator() der:
Original:
The hash template defines a function object that implements a Hash-Funktion. Instances of this function object define an operator() that:
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
1. Einen einzelnen Parameter des Typs Key entgegennimmt.
Original:
1. Accepts a single parameter of type Key.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
2. Einen Wert vom Typ size_t zurückgibt, der den Hash-Wert des Parameters darstellt.
Original:
2. Returns a value of type size_t that represents the hash value of the parameter.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
3. Während der Ausführung keine Exception auslösen.
Original:
3. Does not throw exceptions when called.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
4. Für zwei identische Parameter k1 und k2 gilt: 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).
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
5. Für zwei unterschiedliche Parameter k1 und k2 sollte die Wahrscheinlichkeit, dass std::hash<Key>()(k1) == std::hash<Key>()(k2) minimal sein, näherungsweise 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().
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
Das Hash-Template ist erfüllt die Konzepte CopyConstructible und Destructible.
Original:
The hash template is both CopyConstructible and Destructible.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
Die ungeordnete assoziative Container std::unordered_set, std::unordered_multiset, std::unordered_map, std::unordered_multimap verwenden Spezialisierungen der Vorlage std::hash als Standard-Hash-Funktion .
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.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

Inhaltsverzeichnis

[Bearbeiten] Mitglied Typen

argument_type Key
result_type std::size_t

[Bearbeiten] Member-Funktionen
konstruiert eine Hash-Funktion Objekt
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.

(öffentliche Elementfunktion)
Berechnung der Hash-Wert des Arguments
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.

(öffentliche Elementfunktion)

[Bearbeiten] Standard Spezialisierungen für Grundtypen

definiert in Header <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*>;

[Bearbeiten] Standard Spezialisierungen für Bibliothekstypen

(C++11)
(C++11)
(C++11)
(C++11)
Hash-Unterstützung für 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.

(class Template-Spezialisierung) [edit]
(C++11)
Hash-Unterstützung für 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.

(class Template-Spezialisierung) [edit]
(C++11)
Hash-Unterstützung für 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.

(class Template-Spezialisierung) [edit]
(C++11)
 Hash-Unterstützung für std::unique_ptr
(class Template-Spezialisierung) [edit]
(C++11)
 Hash-Unterstützung für std::shared_ptr
(class Template-Spezialisierung) [edit]
(C++11)
Hash-Unterstützung für 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.

(class Template-Spezialisierung) [edit]
(C++11)
Hash-Unterstützung für 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.

(class Template-Spezialisierung)
(C++11)
Hash-Unterstützung für 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.

(class Template-Spezialisierung)

[Bearbeiten] Beispiele

Demonstriert die Berechnung eines Hash für std::string, ein Typ, der bereits über eine Hash-Spezialisierung .

Original:

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

The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

#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';
}

Output: 

391070135

Veranschaulicht Schaffung einer Hash-Funktion für einen Benutzer definierten Typ. Mit diesem als Template-Parameter für std::unordered_map, std::unordered_set, etc. erfordert auch Spezialisierung 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.

The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

#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";
 
}

Output: 

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

Veranschaulicht, wie std::hash für einen benutzerdefinierten Typ spezialisieren .

Original:

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

The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

#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";
}

Output: 

hash(s) = 32902390710
Von „https://de.cppreference.com/mwiki/index.php?title=cpp/utility/hash&oldid=32116“