std::hash

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实用工具库

类型的支持 (basic types, RTTI, type traits)

（C++11）

hash

（C++11）

关系运算符

rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=

双和元组

pair

tuple

（C++11）

piecewise_construct_t

（C++11）

piecewise_construct

（C++11）

掉期，远期和移动

（C++11）

（C++11）

（C++11）

（C++11）

Defined in header `<functional>`

template< class Key > struct hash; // not defined		（C++11 起）

哈希模板定义一个函数对象，实现了散列函数。这个函数对象的实例定义一个operator()

1。接受一个参数的类型Key.

2。返回一个表示的哈希值的参数的值的类型size_t.

3。不会抛出异常时，称为.

4。两个参数k1k2是平等的，std::hash<Key>()(k1) == std::hash<Key>()(k2).

5。对于两个不同的参数k1k2是不相等的，概率std::hash<Key>()(k1) == std::hash<Key>()(k2)应非常小，接近1.0/std::numeric_limits<size_t>::max().

哈希模板是CopyConstructible和Destructible.

的无序关联式容器std::unordered_set，std::unordered_multiset，std::unordered_map，std::unordered_multimap使用专业的模板std::hash默认的散列函数.


(constructor)	构造一个哈希函数对象 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. （公共成员函数）

operator()	计算哈希的说法 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. （公共成员函数）

[编辑] 标准的专业基本类型

Defined 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*>;

[编辑] 标准库类型专业


std::hash<std::string> std::hash<std::u16string> std::hash<std::u32string> std::hash<std::wstring> （C++11）（C++11）（C++11）（C++11）	字符串哈希支持 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. （类模板专业化） [edit]

std::hash<std::error_code> （C++11）	std::error_code的哈希支持 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. （类模板专业化） [edit]

std::hash<std::bitset> （C++11）	std::bitset的哈希支持 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. （类模板专业化） [edit]

std::hash<std::unique_ptr> （C++11）	std::unique_ptr的哈希支持 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. （类模板专业化） [edit]

std::hash<std::shared_ptr> （C++11）	std::shared_ptr的哈希支持 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. （类模板专业化） [edit]

std::hash<std::type_index> （C++11）	std::type_index的哈希支持 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. （类模板专业化） [edit]

std::hash<std::vector<bool>> （C++11）	std::vector<bool>的哈希支持 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. （类模板专业化）

std::hash<std::thread::id> （C++11）	std::thread::id的哈希支持 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. （类模板专业化）

[编辑] 的例子

演示std::string，已经有一个哈希专业化的类型的哈希计算.

#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

演示如何创建一个用户定义的类型的哈希函数。以此为模板参数std::unordered_map，std::unordered_set等也需要专业化的std::equal_to.

#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

演示如何专门std::hash为用户定义的类型.

#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

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原子操作库（C++11）
线程的支持库（C++11）


`argument_type`	`Key`

`result_type`	std::size_t

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std::hash

目录

[编辑] 会员类型

[编辑] 成员函数

[编辑] 标准的专业基本类型

[编辑] 标准库类型专业

[编辑] 的例子

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