std::tuple_size<std::tuple> - cppreference.com

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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.

## 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

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

std::tuple_size<std::array> | obtains the size of an `array` (class template specialization) [edit]
std::tuple_size<std::pair> (C++11) | obtains the size of a `pair` (class template specialization) [edit]
std::get(std::tuple) | tuple accesses specified element (function template) [edit]
tuple_element | obtains the type of the specified element (class template specialization) [edit]

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