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    std::bad_variant_access

    From cppreference.com
     
    C++
     
    Utilities library
    General utilities
    Relational operators (deprecated in C++20)
     
    std::variant
     
    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:

    (since C++26)

    Member functions

    (constructor)
    		 constructs a new bad_variant_access object
    (public member function)
    operator=
    		 replaces the bad_variant_access object
    (public member function)
    what
    		 returns the explanatory string
    (public member function)

    std::bad_variant_access::bad_variant_access

    bad_variant_access() noexcept;
    		(1) (since C++17) 
    bad_variant_access( const bad_variant_access& other ) noexcept;
    		(2) (since C++17)

    Constructs a new bad_variant_access object with an implementation-defined null-terminated byte string which is accessible through what().

    1) Default constructor.
    2) Copy constructor. If *this and other both have dynamic type std::bad_variant_access then std::strcmp(what(), other.what()) == 0.

    Parameters

    other - another exception object to copy

    std::bad_variant_access::operator=

    bad_variant_access& operator=( const bad_variant_access& other ) noexcept;
    		(since C++17)

    Assigns the contents with those of other.If *this and other both have dynamic type std::bad_variant_access then std::strcmp(what(), other.what()) == 0 after assignment.

    Parameters

    other - another exception object to assign with

    Return value

    *this

    std::bad_variant_access::what

    virtual const char* what() const noexcept;
    		(since C++17)

    Returns the explanatory string.

    Return value

    Pointer to an implementation-defined null-terminated string with explanatory information. The string is suitable for conversion and display as a std::wstring. The pointer is guaranteed to be valid at least until the exception object from which it is obtained is destroyed, or until a non-const member function (e.g. copy assignment operator) on the exception object is called.

    The returned string is encoded with the ordinary literal encoding during constant evaluation.

    		(since C++26)

    Notes

    Implementations are allowed but not required to override what().

    Inherited from std::exception

    Member functions

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

    Example

    Run this code
    #include <iostream>
#include <variant>

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

    (C++17)
    		 reads the value of the variant given the index or the type (if the type is unique), throws on error
    (function template) [edit]
    (C++17)
    		 calls the provided functor with the arguments held by one or more variants
    (function template) [edit]
    (C++26)
    		 calls the provided functor with the argument held by the variant
    (public member function) [edit]