NAME¶

std::get(std::variant) - std::get(std::variant)

Synopsis¶

Defined in header <variant>
template< std::size_t I, class... Types >

constexpr std::variant_alternative_t<I,
std::variant<Types...>>&

get( std::variant<Types...>& v );
template< std::size_t I, class... Types >

constexpr std::variant_alternative_t<I,
std::variant<Types...>>&&

get( std::variant<Types...>&& v );
template< std::size_t I, class... Types >

constexpr const std::variant_alternative_t<I,
std::variant<Types...>>&
(1) (since C++17)
get( const std::variant<Types...>& v );
template< std::size_t I, class... Types >

constexpr const std::variant_alternative_t<I,
std::variant<Types...>>&&

get( const std::variant<Types...>&& v );
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 > (2) (since
constexpr const T& get( const C++17)
std::variant<Types...>& v );
template< class T, class... Types >
constexpr const T&& get( const
std::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 <variant>
#include <string>
#include <iostream>

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_access const& ex)
{
std::cout << ex.what() << ": w contained int, not float\n";
}
}

Possible output:¶

12
42
Unexpected index: w contained int, not float

See also¶

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