std::pair::pair

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

Utilities library

Type support (basic types, RTTI, type traits)

Dynamic memory management

Error handling

Program utilities

Variadic functions

Date and time

Function objects

initializer_list (C++11)

bitset

hash (C++11)

Relational operators

rel_ops::operator!= rel_ops::operator> rel_ops::operator<= rel_ops::operator>=

Pairs and tuples

pair

tuple (C++11)

piecewise_construct_t (C++11)

piecewise_construct (C++11)

Swap, forward and move

swap

forward (C++11)

move (C++11)

move_if_noexcept (C++11)

declval (C++11)

 

std::pair

Member functions

pair::pair

pair::operator=

pair::swap

Non-member functions

make_pair

operator= operator!= operator< operator<= operator> operator>=

std::swap

get (C++11)

Helper classes

tuple_size (C++11)

tuple_element (C++11)

 

pair(); constexpr pair();	(1)	(until C++11) (since C++11)
pair( const T1& x, const T2& y );	(2)
template< class U1, class U2 > pair( U1&& x, U2&& y );	(3)	(since C++11)
template< class U1, class U2 > pair( const pair<U1,U2>& p );	(4)
template< class U1, class U2 > pair( pair<U1,U2>&& p );	(5)	(since C++11)
template< class... Args1, class... Args2 > pair( std::piecewise_construct_t,       std::tuple<Args1...> first_args,       std::tuple<Args2...> second_args );	(6)	(since C++11)
pair( const pair& p ) = default;	(7)
pair( pair&& p ) = default;	(8)	(since C++11)

Constructs a new pair.

1) Default constructor. Value-initializes both elements of the pair, first and second.

2) Initializes first with x and second with y.

3) Initializes first with std::forward<U1>(x) and second with std::forward<U2>(y).

4) Initializes first with p.first and second with p.second.

5) Initializes first with std::move<U1>(p.first) and second with std::move<U2>(p.second).

6) Forwards the elements of first_args to the constructor of first and forwards the elements of second_args to the constructor of second. This is the only non-default constructor that can be used to create a pair of non-copyable non-movable types.

7) Copy constructor is implicitly generated.

8) Move constructor is implicitly generated.

Parameters

x	-	value to initialize the first element of this pair
y	-	value to initialize the second element of this pair
p	-	pair of values used to initialize both elements of this pair
first_args	-	tuple of constructor arguments to initialize the first element of this pair
second_args	-	tuple of constructor arguments to initialize the second element of this pair

Example

run this code

#include <utility>
#include <string>
#include <complex>
#include <tuple>
#include <iostream>
int main()
{
    std::pair<int, float> p1;
    std::cout << "Value-initialized: "
              << p1.first << ", " << p1.second << '\n';
 
    std::pair<int, double> p2(42, 0.123);
    std::cout << "Initialized with two values: "
              << p2.first << ", " << p2.second << '\n';
 
    std::pair<char, int> p4(p2);
    std::cout << "Implicitly converted: "
              << p4.first << ", " << p4.second << '\n';
 
    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'));
    std::cout << "Piecewise constructed: "
              << p6.first << ", " << p6.second << '\n';
}

Output:

Value-initialized: 0, 0
Initialized with two values: 42, 0.123
Implicitly converted: *, 0
Piecewise constructed: (0.123,7.7), aaaaaaaaaa

See also

make_pair	creates a pair object of type, defined by the argument types (function template)