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
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
#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) | |
(C++11) | obtains the type of the elements of pair (class template specialization) |
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