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std::get(std::tuple)

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< cpp‎ | utility‎ | 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 Ith element from the tuple. I must be an integer value in [0sizeof...(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.

[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

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