std::get(std::tuple)
template< std::size_t I, class... Types > typename std::tuple_element<I, tuple<Types...> >::type& |
(1) | (since C++11) (constexpr since C++14) |
template< std::size_t I, class... Types > typename std::tuple_element<I, tuple<Types...> >::type&& |
(2) | (since C++11) (constexpr since C++14) |
template< std::size_t I, class... Types > typename std::tuple_element<I, tuple<Types...> >::type const& |
(3) | (since C++11) (constexpr since C++14) |
template< std::size_t I, class... Types > typename std::tuple_element<I, tuple<Types...> >::type const&& |
(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.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 (function template) | |
(C++11) |
accesses an element of a pair (function template) |
(C++17) |
reads the value of the variant given the index or the type (if the type is unique), throws on error (function template) |