std::tuple_size<std::pair>
From cppreference.com
| 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>> |
(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
| value [static] |
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) |
| operator() (C++14) |
returns value (public member function) |
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 (class template specialization) | |
obtains the size of an array (class template specialization) | |
obtains the type of the elements of pair (class template specialization) |