std::pair

Defined in header `<utility>`
template< class T1, class T2 > struct pair;

std::pair is a class template that provides a way to store two heterogeneous objects as a single unit. A pair is a specific case of a std::tuple with two elements.

If neither T1 nor T2 is a possibly cv-qualified class type with non-trivial destructor, or array thereof, the destructor of pair is trivial.

Template parameters

T1, T2

the types of the elements that the pair stores.

Member types

Member type	Definition
`first_type`	`T1`
`second_type`	`T2`

Member objects

Member name	Type
`first`	`T1`
`second`	`T2`

Member functions

(constructor)	constructs new `pair` (public member function)
operator=	assigns the contents (public member function)
swap (C++11)	swaps the contents (public member function)

Non-member functions

make_pair	creates a `pair` object of type, determined by the argument types (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20)	lexicographically compares the values in the `pair` (function template)
std::swap(std::pair) (C++11)	specializes the `std::swap` algorithm (function template)
get(std::pair) (C++11)	accesses an element of a `pair` (function template)

Helper classes

std::tuple_size<std::pair> (C++11)	obtains the size of a `pair` (class template specialization)
std::tuple_element<std::pair> (C++11)	obtains the type of the elements of `pair` (class template specialization)
std::basic_common_reference<std::pair> (C++23)	determines the common reference type of two `pair`s (class template specialization)
std::common_type<std::pair> (C++23)	determines the common type of two `pair`s (class template specialization)
std::formatter<std::pair> (C++23)	formatting support for `pair` (class template specialization)

Helper specializations

template< class T, class U >
constexpr bool enable_nonlocking_formatter_optimization<std::pair<T, U>> =
    enable_nonlocking_formatter_optimization<T> &&
    enable_nonlocking_formatter_optimization<U>;

(since C++23)

This specialization of std::enable_nonlocking_formatter_optimization enables efficient implementation of std::print and std::println for printing a pair object when both T and U enable it.

Deduction guides(since C++17)

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 2796	C++98	triviality of the destructor of `pair` was unspecified	specified

tuple (C++11)	implements fixed size container, which holds elements of possibly different types (class template)
tie (C++11)	creates a `tuple` of lvalue references or unpacks a tuple into individual objects (function template)