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std::get(std::tuple)

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< cpp‎ | utility‎ | tuple

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get(std::tuple)

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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.

Contents

[edit] Parameters

t - tuple whose contents to extract

[edit] Return value

A reference to the selected element of t.

[edit] Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_tuples_by_type`	`201304L`	(C++14)	Addressing tuples by type (5-8)

[edit] Example

Run this code

#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 )

[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 (by index) C++14 (by type)	there are no overloads for const tuple&&	added these overloads ((4) and (8))

[edit] See also

get(std::array)

(C++11)

accesses an element of an array
(function template) [edit]

(C++11)

accesses an element of a pair
(function template) [edit]

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) [edit]

get(std::ranges::subrange)

(C++20)

obtains iterator or sentinel from a std::ranges::subrange
(function template) [edit]

get(std::complex)

(C++26)

obtains a reference to real or imaginary part from a std::complex
(function template) [edit]

(C++11)

creates a tuple of lvalue references or unpacks a tuple into individual objects
(function template) [edit]

Structured binding (C++17) binds the specified names to sub-objects or tuple elements of the initializer[edit]

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