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std::tuple_element<std::pair>

STD：：元组[医]元素<std：：偶数>

Defined in header ​​
template< class T1, class T2 > struct tuple_element<0, std::pair<T1,T2> >;(1)(since C++11)
template< class T1, class T2 > struct tuple_element<1, std::pair<T1,T2> >;(2)(since C++11)

的部分专门性std::tuple_element对于对，使用类似于元组的语法提供对对%27s元素类型的编译时访问。

成员类型

第一版

*。

成员类型定义

T1型

第二版

成员类型定义

T2型

可能的实施

模板<std：：size[医]TI，type Name T>struct tuple[医]元素；模板<type Name t1，type Name t2>structtuple[医]元素<0，std：：偶数<t1，t2>{使用type=t1；}；模板<type name t1，type Name t2>struct tuple[医]元素<1，std：：对<t1，t2>>{使用类型=t2；}；

*。

例

二次

#include <tuple>
#include <iostream>
#include <string>
 
template <int N, typename T, typename U>
static auto constexpr get(std::pair<T, U> const& pair)
    -> typename std::tuple_element<N, decltype(pair)>::type
{
    return N == 0 ? pair.first : pair.second;
}
 
int main()
{
    auto var = std::make_pair(1, std::string{"one"}
 
    std::cout << get<0>(var) << " = " << get<1>(var
}

二次

产出：

二次

1 = one

二次

另见

tuple_elementobtains the type of the specified element (class template specialization)
std::tuple_element<std::array>obtains the type of the elements of array (class template specialization)
std::tuple_size<std::pair> (C++11)obtains the size of a pair (class template specialization)

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