< cpp‎ | utility‎ | pair

Defined in header <utility>
template< class T1, class T2 >
struct tuple_size<std::pair<T1, T2>>;
(since C++11)
(until C++14)
template <class T1, class T2>

struct tuple_size<std::pair<T1, T2>>

  : std::integral_constant<std::size_t, 2> { };
(since C++14)

The partial specialization of std::tuple_size for pairs provides a compile-time way to obtain the number of elements in a pair, which is always 2, using tuple-like syntax.


Inherited from std::integral_constant

Member constants

the constant value 2
(public static member constant)

Member functions

operator std::size_t
converts the object to std::size_t, returns value
(public member function)

Member types

Type Definition
value_type std::size_t
type std::integral_constant<std::size_t, value>

[edit] Example

#include <iostream>
#include <utility>
#include <tuple>
template<class T>
void test(T t)
    int a[std::tuple_size<T>::value]; // can be used at compile time
    std::cout << std::tuple_size<T>::value << '\n'; // or at run time
int main()
    test(std::make_tuple(1, 2, 3.14));
    test(std::make_pair(1, 3.14));



[edit] See also

obtains the size of tuple at compile time
(class template specialization)
obtains the size of an array
(class template specialization)
obtains the type of the elements of pair
(class template specialization)