std::tuple_size<std::pair>
From cppreference.com
Defined in header
<utility>
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template< class T1, class T2 >
struct tuple_size<std::pair<T1, T2>>; |
(since C++11) (until C++14) |
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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.
Contents |
Inherited from std::integral_constant
Member constants
value
[static]
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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)
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returns value (public member function) |
Member types
Type | Definition |
value_type
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std::size_t
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type
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std::integral_constant<std::size_t, value> |
[edit] 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
[edit] See also
obtains the size of tuple at compile time (class template specialization) |
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obtains the size of an array (class template specialization) |
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(C++11)
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obtains the type of the elements of pair (class template specialization) |