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std::tuple_size<std::tuple>

From cppreference.com
< cpp‎ | utility‎ | tuple
Defined in header <tuple>
template< class T >
class tuple_size; /*undefined*/
(1) (since C++11)
template< class... Types >

class tuple_size< std::tuple<Types...> >

 : public std::integral_constant<std::size_t, sizeof...(Types)> { };
(2) (since C++11)
template< class T >

class tuple_size<const T>

 : public std::integral_constant<std::size_t, tuple_size<T>::value> { };
(3) (since C++11)
template< class T >

class tuple_size< volatile T >

 : public std::integral_constant<std::size_t, tuple_size<T>::value> { };
(4) (since C++11)
template< class T >

class tuple_size< const volatile T >

 : public std::integral_constant<std::size_t, tuple_size<T>::value> { };
(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]
sizeof...(Types)
(public static member constant)

Member functions

operator std::size_t
converts the object to std::size_t, returns value
(public member function)

Member types

Type Definition
value_type std::size_t
type 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

#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) [edit]
obtains the size of a pair
(class template specialization) [edit]
tuple accesses specified element
(function template) [edit]
obtains the type of the specified element
(class template specialization) [edit]