std::get(std::tuple)

 

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Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) Three-way comparison three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)   is_eqis_ltis_lteq (C++20)(C++20)(C++20)   is_neqis_gtis_gteq (C++20)(C++20)(C++20)

General utilities Function objects Bit manipulation (C++20) bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator>    rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)   cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23)

 

std::tuple

Member functions

tuple::tuple

tuple::operator=

tuple::swap

Non-member functions

make_tuple

tie

forward_as_tuple

tuple_cat

operator==operator!=operator<operator<=operator>operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)

swap(std::tuple)

get(std::tuple)

Helper concepts

tuple-like (C++23)

Helper classes

tuple_size<std::tuple>

tuple_element<std::tuple>

uses_allocator<std::tuple>

basic_common_reference<std::tuple> (C++23)

common_type<std::tuple> (C++23)

formatter<std::tuple> (C++23)

ignore

Deduction guides(C++17)

 

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

t

-

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

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 )

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))

See also

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