std::tuple_size<std::tuple>
| Defined in header <tuple>
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| template< class T > class tuple_size; /*undefined*/ |
(1) | (since C++11) |
| template< class... Types > class tuple_size< std::tuple<Types...> > |
(2) | (since C++11) |
| Defined in header <tuple>
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(since C++17) (since C++17) |
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| template< class T > class tuple_size<const T> |
(3) | (since C++11) |
| template< class T > class tuple_size< volatile T > |
(4) | (since C++11) |
| template< class T > class tuple_size< const volatile T > |
(5) | (since C++11) |
Provides access to the number of elements in a tuple as a compile-time constant expression.
In addition to being available via inclusion of the <tuple> header, the templates (3-5) are available when either of the headers <array> or <utility> are included.
All specializations of std::tuple_size satisfy UnaryTypeTrait with BaseCharacteristic std::integral_constant<std::size_t, N> for some N.
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The cv-T templates (3-5) are SFINAE-friendly: if |
(since C++17) |
Contents |
[edit] Helper variable template
| template< class T > inline constexpr std::size_t tuple_size_v = tuple_size<T>::value; |
(since C++17) | |
Inherited from std::integral_constant
Member constants
| value [static] |
sizeof...(Types) (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
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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
#include <iostream> #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)); }
Output:
3
[edit] See also
obtains the size of an array (class template specialization) | |
| (C++11) |
obtains the size of a pair (class template specialization) |
| tuple accesses specified element (function template) | |
| obtains the type of the specified element (class template specialization) |