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std::get(std::tuple)

From cppreference.com
< cpp‎ | utility‎ | tuple
 
 
 
 
template< std::size_t I, class... Types >

typename std::tuple_element<I, tuple<Types...> >::type&

    get( tuple<Types...>& t ) noexcept;
(1) (since C++11)
(constexpr since C++14)
template< std::size_t I, class... Types >

typename std::tuple_element<I, tuple<Types...> >::type&&

    get( tuple<Types...>&& t ) noexcept;
(2) (since C++11)
(constexpr since C++14)
template< std::size_t I, class... Types >

typename std::tuple_element<I, tuple<Types...> >::type const&

    get( const tuple<Types...>& t ) noexcept;
(3) (since C++11)
(constexpr since C++14)
template< std::size_t I, class... Types >

typename std::tuple_element<I, tuple<Types...> >::type const&&

    get( const tuple<Types...>&& t ) noexcept;
(4) (since C++11)
(constexpr since C++14)
template< class T, class... Types >
constexpr T& get(tuple<Types...>& t) noexcept;
(5) (since C++14)
template< class T, class... Types >
constexpr T&& get(tuple<Types...>&& t) noexcept;
(6) (since C++14)
template< class T, class... Types >
constexpr const T& get(const tuple<Types...>& t) noexcept;
(7) (since C++14)
template< class T, class... Types >
constexpr const T&& get(const tuple<Types...>&& t) noexcept;
(8) (since C++14)
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.

Contents

[edit] Parameters

t - tuple whose contents to extract

[edit] Return value

A reference to the selected element of t.

[edit] 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

[edit] Example

#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 (C++14 or later)
    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)

[edit] See also

accesses an element of an array
(function template) [edit]
accesses an element of a pair
(function template) [edit]
reads the value of the variant given the index or the type (if the type is unique), throws on error
(function template) [edit]