std::get(std::pair)(3)

NAME
std::get(std::pair) - std::get(std::pair)

Synopsis
   Defined in header <utility>
   template< std::size_t I, class T1, class T2 >
   typename std::tuple_element<I, std::pair<T1,T2> (1) (since C++11)
   >::type& (constexpr since C++14)
       get( std::pair<T1, T2>& p ) noexcept;
   template< std::size_t I, class T1, class T2 >
   const typename std::tuple_element<I, std::pair<T1,T2> (2) (since C++11)
   >::type& (constexpr since C++14)
       get( const std::pair<T1,T2>& p ) noexcept;
   template< std::size_t I, class T1, class T2 >
   typename std::tuple_element<I, std::pair<T1,T2> (3) (since C++11)
   >::type&& (constexpr since C++14)
       get( std::pair<T1,T2>&& p ) noexcept;
   template< std::size_t I, class T1, class T2 >
   const typename std::tuple_element<I, std::pair<T1,T2> (4) (since C++11)
   >::type&& (constexpr since C++14)
       get( const std::pair<T1,T2>&& p ) noexcept;
   template< class T, class U > (5) (since C++14)
   constexpr T& get( std::pair<T, U>& p ) noexcept;
   template< class T, class U >
   constexpr const T& get( const std::pair<T, U>& p ) (6) (since C++14)
   noexcept;
   template< class T, class U > (7) (since C++14)
   constexpr T&& get( std::pair<T, U>&& p ) noexcept;
   template< class T, class U >
   constexpr const T&& get( const std::pair<T, U>&& p ) (8) (since C++14)
   noexcept;
   template< class T, class U > (9) (since C++14)
   constexpr T& get( std::pair<U, T>& p ) noexcept;
   template< class T, class U >
   constexpr const T& get( const std::pair<U, T>& p ) (10) (since C++14)
   noexcept;
   template< class T, class U > (11) (since C++14)
   constexpr T&& get( std::pair<U, T>&& p ) noexcept;
   template< class T, class U >
   constexpr const T&& get( const std::pair<U, T>&& p ) (12) (since C++14)
   noexcept;
   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) there are no overloads for const the overloads are added
            C++14 (by type) pair&&

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