std::tuple_size<std::tuple>
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tuple_size<std::tuple>
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Defined in header
<tuple>
template< class... Types >
(since C++11)
struct tuple_size< std::tuple <Types...> >
Provides access to the number of elements in a tuple as a compile-time constant expression.
Contents
[edit] Helper variable template
template< class T >
constexpr std::size_t tuple_size_v = tuple_size<T>::value;
(since C++17)
constexpr std::size_t tuple_size_v = tuple_size<T>::value;
Inherited from std::integral_constant
Member constants
value
[static]
sizeof...(Types) (public static member constant)
Member functions
operator()
(C++14)
(public member function)
Member types
Type
Definition
value_type
std::size_t
type
std::integral_constant <std::size_t, value>
[edit] Example
Run this code
#include <iostream> #include <tuple> template <class T> void test(T value) { int a[std::tuple_size_v <T>]; // can be used at compile time std::cout << std::tuple_size <T>{} << ' ' // or at run time << sizeof a << ' ' << sizeof value << '\n'; } int main() { test(std::make_tuple (1, 2, 3.14)); }
Possible output:
3 12 16
[edit] See also
Structured binding (C++17)
binds the specified names to sub-objects or tuple elements of the initializer[edit]