W3cubDocs

std::get(std::tuple)

Defined in header `<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.

Parameters

tuple whose contents to extract

Return value

A reference to the selected element of t.

Notes

Feature-test macro	Value	Std	Comment
`__cpp_lib_tuples_by_type`	`201304L`	(C++14)	for type-based access

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)

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 (by index) C++14 (by type)	there are no overloads for const tuple&&	the overloads are added

Structured binding (C++17)	binds the specified names to sub-objects or tuple elements of the initializer
std::get(std::array) (C++11)	accesses an element of an `array` (function template)
std::get(std::pair) (C++11)	accesses an element of a `pair` (function template)
std::get(std::variant) (C++17)	reads the value of the variant given the index or the type (if the type is unique), throws on error (function template)
get(std::ranges::subrange) (C++20)	obtains iterator or sentinel from a `std::ranges::subrange` (function template)