std::tuple_element<std::pair>

C++

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Named requirements

Language support library

Concepts library (C++20)

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Regular expressions library (C++11)

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Technical Specifications

Utilities library

Type support (basic types, RTTI, type traits)
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initializer_list (C++11)
bitset
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rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
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strong_order weak_order partial_order strong_equal weak_equal	strong_ordering weak_ordering partial_ordering strong_equality weak_equality	is_eqis_neqis_ltis_lteqis_gtis_gteq
common_comparison_category
Common vocabulary types
pair tuple (C++11) apply (C++17) make_from_tuple (C++17)	optional (C++17) any (C++17) variant (C++17)
Swap, forward and move
swap
exchange (C++14)
forward (C++11)
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std::pair

Member functions

pair::pair

pair::operator=

pair::swap

Non-member functions

make_pair

operator==operator!=operator<operator<=operator>operator>=

std::swap

get (C++11)

Deduction guides(C++17)

Helper classes

tuple_size (C++11)

tuple_element (C++11)

Defined in header <utility>
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)

The partial specializations of std::tuple_element for pairs provide compile-time access to the types of the pair's elements, using tuple-like syntax.

Member types

First version
Member type	Definition
type	T1
Second version
Member type	Definition
type	T2

Possible implementation

template<std::size_t I, typename T> struct tuple_element; template<typename T1, typename T2> struct tuple_element<0, std::pair<T1,T2> > { using type = T1; }; template<typename T1, typename T2> struct tuple_element<1, std::pair<T1,T2> > { using type = T2; };

Example

Run this code

#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);
}

Output:

1 = one

See also

tuple_element	obtains 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)