std::tuple_size<std::pair> (3) - Linux Man Pages

std::tuple_size<std::pair>: std::tuple_size<std::pair>

NAME

std::tuple_size<std::pair> - std::tuple_size<std::pair>

Synopsis


Defined in header <utility>
template< class T1, class T2 > (since C++11)
struct tuple_size<std::pair<T1, T2>>; (until C++14)
template <class T1, class T2>
struct tuple_size<std::pair<T1, T2>> (since C++14)
: std::integral_constant<std::size_t, 2> { };


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


value the constant value 2
         (public static member constant)
[static]

Member functions


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


operator() returns value
                     (public member function)
(C++14)

Member types


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

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


                              obtains the size of tuple at compile time
tuple_size (class template specialization)
                              obtains the size of an array
std::tuple_size<std::array> (class template specialization)


std::tuple_element<std::pair> obtains the type of the elements of pair
                              (class template specialization)
(C++11)