std::get(std::variant)

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Utilities library

Language support

Type support (basic types, RTTI)

Library feature-test macros(C++20)

Program utilities

Variadic functions

initializer_list

(C++11)

is_constant_evaluated

(C++20)

is_within_lifetime

(C++26)

source_location

(C++20)

Coroutine support(C++20)

Contract support(C++26)

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)

(C++20)

(C++20)

(C++20)

(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)

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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 andtype 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)

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std::variant

Member functions
variant::variant
variant::~variant
variant::operator=
Observers
variant::index
variant::valueless_by_exception
Modifiers
variant::emplace
variant::swap
Visitation
variant::visit (C++26)
Non-member functions
visit(std::variant)
holds_alternative
get(std::variant)
get_if
operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)
swap(std::variant)
Helper classes
monostate
bad_variant_access
variant_size
variant_alternative
hash<std::variant>
Helper objects
variant_npos

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Defined in header`<variant>`
	(1)	(since C++17)
template<std::size_t I,class...Types> constexprstd::variant_alternative_t<I,std::variant<Types...>>& get(std::variant<Types...>& v);
template<std::size_t I,class...Types> constexprstd::variant_alternative_t<I,std::variant<Types...>>&& get(std::variant<Types...>&& v);
template<std::size_t I,class...Types> constexprconststd::variant_alternative_t<I,std::variant<Types...>>& get(conststd::variant<Types...>& v);
template<std::size_t I,class...Types> constexprconststd::variant_alternative_t<I,std::variant<Types...>>&& get(conststd::variant<Types...>&& v);
			(2)	(since C++17)
template<class T,class...Types> constexpr T& get(std::variant<Types...>& v);
template<class T,class...Types> constexpr T&& get(std::variant<Types...>&& v);
template<class T,class...Types> constexprconst T& get(conststd::variant<Types...>& v);
template<class T,class...Types> constexprconst T&& get(conststd::variant<Types...>&& v);

1) Index-based value accessor: Ifv.index()== I, returns a reference to the value stored inv. Otherwise, throwsstd::bad_variant_access. The call is ill-formed ifI is not a valid index in the variant.

2) Type-based value accessor: Ifv holds the alternativeT, returns a reference to the value stored inv. Otherwise, throwsstd::bad_variant_access. The call is ill-formed ifT is not a unique element ofTypes....

[edit]Template parameters

I	-	index to look up
T	-	unique type to look up
Types...	-	types forming the`variant`

[edit]Parameters

v - avariant

[edit]Return value

Reference to the value stored in the variant.

[edit]Exceptions

1,2) Throwsstd::bad_variant_access on errors.

[edit]Example

Run this code

#include <iostream>#include <string>#include <variant> int main(){std::variant<int,float> v{12}, w;std::cout<< std::get<int>(v)<<'\n';    w= std::get<int>(v);    w= std::get<0>(v);// same effect as the previous line //  std::get<double>(v); // error: no double in [int, float]//  std::get<3>(v);      // error: valid index values are 0 and 1 try{        w=42.0f;std::cout<< std::get<float>(w)<<'\n';// ok, prints 42        w=42;std::cout<< std::get<float>(w)<<'\n';// throws}catch(std::bad_variant_accessconst& ex){std::cout<< ex.what()<<": w contained int, not float\n";}}

Possible output:

1242Unexpected index: w contained int, not float

[edit]See also

get_if (C++17)	obtains a pointer to the value of a pointed-to`variant` given the index or the type (if unique), returns null on error (function template)[edit]
get(std::tuple) (C++11)	tuple accesses specified element (function template)[edit]
get(std::array) (C++11)	accesses an element of an`array` (function template)[edit]
get(std::pair) (C++11)	accesses an element of a`pair` (function template)[edit]
get(std::ranges::subrange) (C++20)	obtains iterator or sentinel from astd::ranges::subrange (function template)[edit]
get(std::complex) (C++26)	obtains a reference to real or imaginary part from astd::complex (function template)[edit]