std:: get (std::pair)

From cppreference.com
C++
Utilities library
General utilities
Relational operators (deprecated in C++20)
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

Run this code 
#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)
(C++26)
obtains a reference to real or imaginary part from a std::complex
(function template)
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