table of contents
std::get(std::variant)(3) | C++ Standard Libary | std::get(std::variant)(3) |
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)
2022.07.31 | http://cppreference.com |