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Difference between revisions of "cpp/utility/pair/get"

From cppreference.com
< cpp‎ | utility‎ | pair
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template <class T, class U>
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template< class T, class U >
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constexpr T& get(std::pair<T, U>& p) noexcept;
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constexpr T& get( std::pair<T, U>& p ) noexcept;
 
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template <class T, class U>
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template< class T, class U >
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constexpr const T& get(const std::pair<T, U>& p) noexcept;
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constexpr const T& get( const std::pair<T, U>& p ) noexcept;
 
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template <class T, class U>
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template< class T, class U >
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constexpr T&& get(std::pair<T, U>&& p) noexcept;
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constexpr T&& get( std::pair<T, U>&& p ) noexcept;
 
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template <class T, class U>
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template< class T, class U >
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constexpr const T&& get(const std::pair<T, U>&& p) noexcept;
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constexpr const T&& get( const std::pair<T, U>&& p ) noexcept;
 
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template <class T, class U>
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template< class T, class U >
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constexpr T& get(std::pair<U, T>& p) noexcept;
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constexpr T& get( std::pair<U, T>& p ) noexcept;
 
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template <class T, class U>
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template< class T, class U >
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constexpr const T& get(const std::pair<U, T>& p) noexcept;
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constexpr const T& get( const std::pair<U, T>& p ) noexcept;
 
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template <class T, class U>
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template< class T, class U >
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constexpr T&& get(std::pair<U, T>&& p) noexcept;
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constexpr T&& get( std::pair<U, T>&& p ) noexcept;
 
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template <class T, class U>
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template< class T, class U >
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constexpr const T&& get(const std::pair<U, T>&& p) noexcept;
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constexpr const T&& get( const std::pair<U, T>&& p ) noexcept;
 
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Revision as of 00:43, 12 February 2024

 
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.

Contents

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[edit]
(C++11)
 tuple accesses specified element
(function template) [edit]
(C++11)
 accesses an element of an array
(function template) [edit]
(C++17)
 reads the value of the variant given the index or the type (if the type is unique), throws on error
(function template) [edit]
(C++20)
 obtains iterator or sentinel from a std::ranges::subrange
(function template) [edit]
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