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std::get(std::pair)

Defined in header <utility> 
template< std::size_t I, class T1, class T2 >
typename std::tuple_element<I, std::pair<T1,T2> >::type&
    get( std::pair<T1, T2>& p ) noexcept;
 (1) (since C++11)
(constexpr since C++14) 
template< std::size_t I, class T1, class T2 >
const typename std::tuple_element<I, std::pair<T1,T2> >::type&
    get( const std::pair<T1,T2>& p ) noexcept;
 (2) (since C++11)
(constexpr since C++14) 
template< std::size_t I, class T1, class T2 >
typename std::tuple_element<I, std::pair<T1,T2> >::type&&
    get( std::pair<T1,T2>&& p ) noexcept;
 (3) (since C++11)
(constexpr since C++14) 
template< std::size_t I, class T1, class T2 >
const typename std::tuple_element<I, std::pair<T1,T2> >::type&&
    get( const std::pair<T1,T2>&& p ) noexcept;
 (4) (since C++11)
(constexpr since C++14) 
template <class T, class U>
constexpr T& get(std::pair<T, U>& p) noexcept;
 (5) (since C++14) 
template <class T, class U>
constexpr const T& get(const std::pair<T, U>& p) noexcept;
 (6) (since C++14) 
template <class T, class U>
constexpr T&& get(std::pair<T, U>&& p) noexcept;
 (7) (since C++14) 
template <class T, class U>
constexpr const T&& get(const std::pair<T, U>&& p) noexcept;
 (8) (since C++14) 
template <class T, class U>
constexpr T& get(std::pair<U, T>& p) noexcept;
 (9) (since C++14) 
template <class T, class U>
constexpr const T& get(const std::pair<U, T>& p) noexcept;
 (10) (since C++14) 
template <class T, class U>
constexpr T&& get(std::pair<U, T>&& p) noexcept;
 (11) (since C++14) 
template <class T, class U>
constexpr const T&& get(const std::pair<U, T>&& p) noexcept;
 (12) (since C++14)

Extracts an element from the pair using tuple-like interface.

1-4) The index-based overloads fail to compile if the index I is neither ​0​ nor 1.
5-12) The type-based overloads fail to compile if the types T and U are the same.

Parameters

p - pair whose contents to extract

Return value

1-4) Returns a reference to p.first if I == 0 and a reference to p.second if I == 1.
5-8) Returns a reference to p.first.
9-12) Returns a reference to p.second.

Example

#include <iostream>
#include <utility>
 
int main()
{
    auto p = std::make_pair(1, 3.14);
    std::cout << '(' << std::get<0>(p) << ", " << std::get<1>(p) << ")\n";
    std::cout << '(' << std::get<int>(p) << ", " << std::get<double>(p) << ")\n";
}

Output:

(1, 3.14)
(1, 3.14)

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2485 C++11 (by index)
C++14 (by type) 		there are no overloads for const pair&& the overloads are added

See also

Structured binding (C++17) binds the specified names to sub-objects or tuple elements of the initializer
(C++11)
 tuple accesses specified element
(function template)
(C++11)
 accesses an element of an array
(function template)
(C++17)
 reads the value of the variant given the index or the type (if the type is unique), throws on error
(function template)
(C++20)
 obtains iterator or sentinel from a std::ranges::subrange
(function template)

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