std::tuple_size<std::tuple>

Defined in header `<tuple>`
template< class... Types > struct tuple_size< std::tuple<Types...> > : std::integral_constant<std::size_t, sizeof...(Types)> { };		(since C++11)

Provides access to the number of elements in a tuple as a compile-time constant expression.

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`	std::size_t
`type`	std::integral_constant<std::size_t, value>

Example

#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

Structured binding (C++17)	binds the specified names to sub-objects or tuple elements of the initializer
tuple_size (C++11)	obtains the number of elements of a tuple-like type (class template)
std::tuple_size<std::pair> (C++11)	obtains the size of a `pair` (class template specialization)
std::tuple_size<std::array> (C++11)	obtains the size of an `array` (class template specialization)
std::tuple_size<std::ranges::subrange> (C++20)	obtains the number of components of a `std::ranges::subrange` (class template specialization)
get(std::tuple) (C++11)	tuple accesses specified element (function template)

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/utility/tuple/tuple_size