std::get(std::variant)

 

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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

 

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: If v.index()== I, returns a reference to the value stored in v. Otherwise, throws std::bad_variant_access. The call is ill-formed if I is not a valid index in the variant.

2) Type-based value accessor: If v holds the alternative T, returns a reference to the value stored in v. Otherwise, throws std::bad_variant_access. The call is ill-formed if T is not a unique element of Types....

Template parameters

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

Parameters

v

-

a variant

Return value

Reference to the value stored in the variant.

Exceptions

1,2) Throws std::bad_variant_access on errors.

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:

12 42 Unexpected index: w contained int, not float

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)
get(std::tuple) (C++11)	tuple accesses specified element (function template)
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::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)