std::get(std::pair)

 

C++

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Utilities library

Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Dynamic memory management Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) Three-way comparison (C++20) three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)    is_eqis_neqis_ltis_lteqis_gtis_gteq (C++20)(C++20)(C++20)(C++20)(C++20)(C++20)

General utilities Date and time Function objects Formatting library (C++20) bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator> rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)    cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23) Elementary string conversions to_chars (C++17) from_chars (C++17) chars_format (C++17)

 

std::pair

Member functions

pair::pair

pair::operator=

pair::swap (C++11)

Non-member functions

make_pair

operator==operator!=operator<operator<=operator>operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)

std::swap (C++11)

get (C++11)

Deduction guides(C++17)

Helper classes

tuple_size (C++11)

tuple_element (C++11)

basic_common_reference (C++23)

common_type (C++23)

piecewise_construct_t (C++11)

 

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