std::tuple_element<std::pair>

 

C++

Language

Standard library headers

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Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

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Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)

Dynamic memory management

Error handling

Program utilities

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Date and time

Function objects

initializer_list (C++11)

bitset

hash (C++11)

Relational operators

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

Pairs and tuples

pair

tuple (C++11)

piecewise_construct_t (C++11)

piecewise_construct (C++11)

integer_sequence (C++14)

Swap, forward and move

swap

exchange (C++14)

forward (C++11)

move (C++11)

move_if_noexcept (C++11)

Type operations

declval (C++11)

as_const (C++17)

 

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)

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)