std::get(std::tuple)

Defined in header `<tuple>`
template< std::size_t I, class... Types > typename std::tuple_element<I, std::tuple<Types...>>::type& get( std::tuple<Types...>& t ) noexcept;	(1)	(since C++11) (constexpr since C++14)
template< std::size_t I, class... Types > typename std::tuple_element<I, std::tuple<Types...>>::type&& get( std::tuple<Types...>&& t ) noexcept;	(2)	(since C++11) (constexpr since C++14)
template< std::size_t I, class... Types > const typename std::tuple_element<I, std::tuple<Types...>>::type& get( const std::tuple<Types...>& t ) noexcept;	(3)	(since C++11) (constexpr since C++14)
template< std::size_t I, class... Types > const typename std::tuple_element<I, std::tuple<Types...>>::type&& get( const std::tuple<Types...>&& t ) noexcept;	(4)	(since C++11) (constexpr since C++14)
template< class T, class... Types > constexpr T& get( std::tuple<Types...>& t ) noexcept;	(5)	(since C++14)
template< class T, class... Types > constexpr T&& get( std::tuple<Types...>&& t ) noexcept;	(6)	(since C++14)
template< class T, class... Types > constexpr const T& get( const std::tuple<Types...>& t ) noexcept;	(7)	(since C++14)
template< class T, class... Types > constexpr const T&& get( const std::tuple<Types...>&& t ) noexcept;	(8)	(since C++14)

1-4) Extracts the I^th 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	Feature
`__cpp_lib_tuples_by_type`	`201304L`	(C++14)	Addressing tuples by type (5-8)

Example

#include <cassert>
#include <iostream>
#include <string>
#include <tuple>

int main()
{
    auto x = std::make_tuple(1, "Foo", 3.14);
    
    // Index-based access
    std::cout << "( " << std::get<0>(x)
              << ", " << std::get<1>(x)
              << ", " << std::get<2>(x)
              << " )\n";
    
    // Type-based access (since C++14)
    std::cout << "( " << std::get<int>(x)
              << ", " << std::get<const char*>(x)
              << ", " << std::get<double>(x)
              << " )\n";

    const std::tuple<int, const int, double, double> y(1, 2, 6.9, 9.6);
    const int& i1 = std::get<int>(y); // OK: not ambiguous
    assert(i1 == 1);
    const int& i2 = std::get<const int>(y); // OK: not ambiguous
    assert(i2 == 2);
    // const double& d = std::get<double>(y); // Error: ill-formed (ambiguous)

    // Note: std::tie and structured binding can be
    // used to unpack a tuple into individual objects.
}

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 consttuple&&	added these overloads ((4) and (8))

get(std::array) (C++11)	accesses an element of an `array` (function template)
get(std::pair) (C++11)	accesses an element of a `pair` (function template)
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)
get(std::complex) (C++26)	obtains a reference to real or imaginary part from a `std::complex` (function template)
tie (C++11)	creates a `tuple` of lvalue references or unpacks a tuple into individual objects (function template)
Structured binding (C++17)	binds the specified names to sub-objects or tuple elements of the initializer