sizeof... operator

cppreference sizeof... operator

Queries the number of elements in a parameter pack.

Example

#include <iostream>
#include <array>
#include <type_traits>

template<typename ... Ts>
constexpr auto make_array(Ts&&... ts) -> std::array<std::common_type_t<Ts...>,sizeof...(ts)>
{
    return {    std::forward<Ts>(ts)...};
}

int main()
{
    auto b = make_array(1, 2, 3);
    std::cout << b.size() << '\n';
    for (auto i : b)
        std::cout << i << ' ';
}
// g++ --std=c++11 test.cpp