std::tuple_size<std::tuple>
From cppreference.com
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.
Contents |
Inherited from std::integral_constant
Member constants
value
[static]
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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)
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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] Notes
All specializations of std::tuple_size
satisfy UnaryTypeTrait
with BaseCharacteristic std::integral_constant<std::size_t, N>
for some N
.
[edit] Example
Run this code
#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) |
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(C++11)
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obtains the size of a pair (class template specialization) |
tuple accesses specified element (function template) |
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obtains the type of the specified element (class template specialization) |
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(library fundamentals TS)
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variable template alias of std::tuple_size::value (variable template) |