# std::pair

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< cpp‎ | utility

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

### See also

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)

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