std::bad_variant_access

 

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std::variant

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bad_variant_access

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Defined in header <variant>
class bad_variant_access : public std::exception		(since C++17)

std::bad_variant_access is the type of the exception thrown in the following situations:

• std::get(std::variant) called with an index or type that does not match the currently active alternative
• std::visit called to visit a variant that is valueless_by_exception

Member functions

(constructor)

constructs the bad_variant_access object (public member function)

std::bad_variant_access ::bad_variant_access()

bad_variant_access() noexcept;

Constructs a new instance of std::bad_variant_access.

Parameters

(none)

Inherited from std::exception

Member functions

(destructor) [virtual]	destroys the exception object (virtual public member function of std::exception)
what [virtual]	returns an explanatory string (virtual public member function of std::exception)

Example

Run this code

#include <variant>
#include <iostream>
 
int main()
{
    std::variant<int, float> v;
    v = 12;
    try {
      std::get<float>(v);
    }
    catch(const std::bad_variant_access& e) {
        std::cout << e.what() << '\n';
    }
}

Possible output:

bad_variant_access

See also

std::get(std::variant) (C++17)	reads the value of the variant given the index or the type (if the type is unique), throws on error (function template)
visit (C++17)	calls the provided functor with the arguments held by one or more variants (function template)