std::tuple_size<std::pair>

 

C++

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tuple_size (C++11)

tuple_element (C++11)

 

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

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.

Members
value [static]	integral constant with value 2 (public static member constant)

Example

run this code

#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));
}

Output:

3
2

See also

tuple_size	obtains the size of tuple at compile time (class template specialization)
std::tuple_size<std::array>	obtains the size of an array (class template specialization)
std::tuple_element<std::pair> (C++11)	obtains the type of the elements of pair (class template specialization)