std::get(std::tuple) (3) Linux Manual Page

std::get(std::tuple) – std::get(std::tuple)

Synopsis

template <std::size_t I, class... Types>
(since C++ 11)

    typename std::tuple_element<I, tuple<Types...>>::type &(1)(constexpr since C++ 14)

        get(tuple<Types...> &t) noexcept;

template <std::size_t I, class... Types>
    (since C++ 11)

        typename std::tuple_element<I, tuple<Types...>>::type
    && (2)(constexpr since C++ 14)

           get(tuple<Types...> &&t) noexcept;

template <std::size_t I, class... Types>
(since C++ 11)

    typename std::tuple_element<I, tuple<Types...>>::type const &(3)(constexpr since C++ 14)

        get(const tuple<Types...> &t) noexcept;

template <std::size_t I, class... Types>
    (since C++ 11)

        typename std::tuple_element<I, tuple<Types...>>::type const
    && (4)(constexpr since C++ 14)

           get(const tuple<Types...> &&t) noexcept;

template <class T, class... Types>
(5)(since C++ 14)

    constexpr T &get(tuple<Types...> &t) noexcept;

template <class T, class... Types>
(6)(since C++ 14)

    constexpr T &&get(tuple<Types...> &&t) noexcept;

template <class T, class... Types>
(7)(since C++ 14)

    constexpr const T &get(const tuple<Types...> &t) noexcept;

template <class T, class... Types>
(8)(since C++ 14)

    constexpr const T &&get(const tuple<Types...> &&t) noexcept;

1-4) Extracts the Ith element from the tuple. I must be an integer value in [0, sizeof…(Types)).
5-8) Extracts the element of the tuple t whose type is T. Fails to compile unless the tuple has exactly one element of that type.

Parameters

t – tuple whose contents to extract

Return value

A reference to the selected element of t.
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
LWG_2485 C++11 there are no overloads for const tuple&& the overloads are added

Example

// Run this code

#include <iostream>

#include <string>

#include <tuple>
int main()

{
    auto t = std::make_tuple(1, "Foo", 3.14);
    // index-based access
    std::cout << "(" << std::get<0>(t) << ", " << std::get<1>(t)
              << ", " << std::get<2>(t) << ")\n";
    // type-based access
    std::cout << "(" << std::get<int>(t) << ", " << std::get<const char *>(t)
              << ", " << std::get<double>(t) << ")\n";
    // Note: std::tie and structured binding may also be used to decompose a tuple
}

Output:

  (1, Foo, 3.14)
  (1, Foo, 3.14)

See also

                       accesses an element of an array
std::get(std::array) (function template)
std::get(std::pair) accesses an element of a pair
                       (function template)
(C++11)
std::get(std::variant) reads the value of the variant given the index or the type (if the type is unique), throws on error
                       (function template)
(C++17)