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std::pair::pair cppreference.com
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std::pair::pair

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(C++20)
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(C++11)
(C++20)
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(C++11)
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(C++11)
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(C++20)
(C++11)
( C++20)
(C++20)(C++20)(C++20)    
(C++20)
(C++20)
(C++14)
(C++11)
(C++23)
(C++11)
(C++23)
(C++11)
(C++11)
(C++17)
(C++11)
(C++17)
(C++17)
(C++17)
(C++11)
(C++11)
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(C++17)
 
std::pair
 
<tbody> </tbody> <tbody class="t-dcl-rev t-dcl-rev-num "> </tbody><tbody> </tbody> <tbody class="t-dcl-rev t-dcl-rev-num "> </tbody><tbody> </tbody> <tbody class="t-dcl-rev t-dcl-rev-num "> </tbody><tbody> </tbody> <tbody class="t-dcl-rev t-dcl-rev-num "> </tbody><tbody> </tbody> <tbody class="t-dcl-rev t-dcl-rev-num "> </tbody><tbody> </tbody> <tbody class="t-dcl-rev t-dcl-rev-num "> </tbody><tbody> </tbody>
(1)
pair();
 ( C++11)
constexpr pair();
 ( C++11)
(conditionally explicit)
(2)
pair( const T1& x, const T2& y );
 ( C++11)
pair( const T1& x, const T2& y );
 ( C++11)
( C++14)
(conditionally explicit)
constexpr pair( const T1& x, const T2& y );
 ( C++14)
(conditionally explicit)
(3)
template< class U1, class U2 > pair( U1&& x, U2&& y );
 ( C++11)
( C++14)
(conditionally explicit)
template< class U1, class U2 > constexpr pair( U1&& x, U2&& y );
 ( C++14)
( C++23)
(conditionally explicit)
template< class U1 = T1, class U2 = T2 > constexpr pair( U1&& x, U2&& y );
 ( C++23)
(conditionally explicit)
template< class U1, class U2 > constexpr pair( pair<U1, U2>& p );
 (4) ( C++23)
(conditionally explicit)
(5)
template< class U1, class U2 > pair( const pair<U1, U2>& p );
 ( C++11)
template< class U1, class U2 > pair( const pair<U1, U2>& p );
 ( C++11)
( C++14)
(conditionally explicit)
template< class U1, class U2 > constexpr pair( const pair<U1, U2>& p );
 ( C++14)
(conditionally explicit)
(6)
template< class U1, class U2 > pair( pair<U1, U2>&& p );
 ( C++11)
( C++14)
(conditionally explicit)
template< class U1, class U2 > constexpr pair( pair<U1, U2>&& p );
 ( C++14)
(conditionally explicit)
template< class U1, class U2 > constexpr pair( const pair<U1, U2>&& p );
 (7) ( C++23)
(conditionally explicit)
template< pair-like P > constexpr pair ( P&& u );
 (8) ( C++23)
(conditionally explicit)
(9)
template< class... Args1, class... Args2 > pair( std::piecewise_construct_t, std::tuple<Args1...> first_args, std::tuple<Args2...> second_args );
 ( C++11)
( C++20)
template< class... Args1, class... Args2 > constexpr pair( std::piecewise_construct_t, std::tuple<Args1...> first_args, std::tuple<Args2...> second_args );
 ( C++20)
pair( const pair& p ) = default;
 (10)
pair( pair&& p ) = default;
 (11) ( C++11)

pair.

1) . pair, first second.

, std::is_default_constructible_v<T1> std::is_default_constructible_v<T2> true.

explicit , T1, T2 .

( C++11)
2) first x second y.

, std::is_copy_constructible_v<T1> std::is_copy_constructible_v<T2> true.

explicit , std::is_convertible_v<const T1&, T1> false std::is_convertible_v<const T2&, T2> false.

( C++11)
3) first std::forward<U1>(x) second std::forward<U2>(y).
, std::is_constructible_v<T1, U1> std::is_constructible_v<T2, U2> true.
explicit , std::is_convertible_v<U1, T1> false std::is_convertible_v<U2, T2> false.

, first second .

( C++23)
4) first p.first second p.second.
, std::is_constructible_v<T1, U1&> std::is_constructible_v<T2, U2&> true.
explicit , std::is_convertible_v<U1&, T1> false std::is_convertible_v<U2&, T2> false.
, first second .
5) first p.first second p.second.

, std::is_constructible_v<T1, const U1&> std::is_constructible_v<T2, const U2&> true.

explicit , std::is_convertible_v<const U1&, T1> false std::is_convertible_v<const U2&, T2> false.

( C++11)

, first second .

( C++23)
6) first std::forward<U1>(p.first) second std::forward<U2>(p.second).
, std::is_constructible_v<T1, U1> std::is_constructible_v<T2, U2> true.
explicit , std::is_convertible_v<U1, T1> false std::is_convertible_v<U2, T2> false.

, first second .

( C++23)
7) first std::forward<const U1>(p.first) second std::forward<const U2>(p.second).
, std::is_constructible_v<T1, U1> std::is_constructible_v<T2, U2> true.
explicit , std::is_convertible_v<const U1, T1> false std::is_convertible_v<const U2, T2> false.
, first second .
8) u1 std::get<0>(std::forward(u)) u2 std::get<1>(std::forward(u)), U1 U2 . first u1 second u2.
,
  • std::remove_cvref(P) std::ranges::subrange,
  • std::is_constructible_v<T1, U1> true,
  • std::is_constructible_v<T2, U2 true.
explicit , std::is_convertible_v<U1, T1> false std::is_convertible_v<U2, T2> false.
, first second .
9) first_args first second_args second. , . , first second .
10) ( C++11) constexpr, constexpr ( C++11).
11) constexpr, constexpr.

x pair
y pair
p pair , pair
u pair-like, pair
first_args pair
second_args pair

, (, ) . 

#include <complex>
#include <iostream>
#include <string>
#include <tuple>
#include <utility>

int main()
{
    auto print = [](auto rem, auto const& pair)
    {
        std::cout << rem << "(" << pair.first << ", " << pair.second << ")\n";
    };
    
    std::pair<int, float> p1;
    print("(1)  : ", p1);
    
    std::pair<int, double> p2{42, 3.1415};
    print("(2)   : ", p2);
    
    std::pair<char, int> p4{p2};
    print("(4)  : ", p4);
    
    std::pair<std::complex<double>, std::string> p6
        {std::piecewise_construct, std::forward_as_tuple(0.123, 7.7),
            std::forward_as_tuple(10, 'a')};
    print("(8)  : ", p6);
}

: 

(1)  : (0, 0)
(2)   : (42, 3.1415)
(4)  : (*, 3)
(8)  : ((0.123,7.7), aaaaaaaaaa)

C++:

LWG 265 C++98
first second T1() T2()
( , T1 T2
CopyConstructible) 		first second
LWG 2510 C++11 -
WG C++11 ,
-

pair,
( ) []
tuple
(public - std::tuple) []
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