std::get(std::variant) - cppreference.com (original) (raw)

| Defined in header | | | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------- | | | (1) | (since C++17) | | | 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...>>& 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 ); | | | | (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 > constexpr const T& get( const 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....

Contents

• 1 Template parameters
• 2 Parameters
• 3 Return value
• 4 Exceptions
• 5 Example
• 6 See also

[edit] Template parameters

[edit] Parameters

[edit] Return value

Reference to the value stored in the variant.

[edit] Exceptions

[edit] Example

#include #include #include   int main() { std::variant<int, float> v{12}, w; std::cout << std::get(v) << '\n'; w = std::get(v); w = std::get<0>(v); // same effect as the previous line   // std::get(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(w) << '\n'; // ok, prints 42 w = 42; std::cout << std::get(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

[edit] See also