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Showing content from https://en.cppreference.com/w/cpp/language/../error/error_code/../../types/bad_cast.html below:

std::bad_cast - cppreference.com

An exception of this type is thrown when a dynamic_cast to a reference type fails the run-time check (e.g., because the types are not related by inheritance), and also from std::use_facet if the requested facet does not exist in the locale.

Inheritance diagram

[edit] Member functions constructs a new bad_cast object
(public member function) replaces the bad_cast object
(public member function) returns the explanatory string
(public member function) std::bad_cast::bad_cast (1)

bad_cast() throw();

(until C++11)

bad_cast() noexcept;

(since C++11)
(constexpr since C++26) (2)

bad_cast( const bad_cast& other ) throw();

(until C++11)

bad_cast( const bad_cast& other ) noexcept;

(since C++11)
(constexpr since C++26)

Constructs a new bad_cast 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_cast then std::strcmp(what(), other.what()) == 0.(since C++11) Parameters other - another exception object to copy std::bad_cast::operator=

bad_cast& operator=( const bad_cast& other ) throw();

(until C++11)

bad_cast& operator=( const bad_cast& other ) noexcept;

(since C++11)
(constexpr since C++26)

Assigns the contents with those of other. If *this and other both have dynamic type std::bad_cast then std::strcmp(what(), other.what()) == 0 after assignment.(since C++11)

Parameters other - another exception object to assign with Return value

*this

std::bad_cast::what

virtual const char* what() const throw();

(until C++11)

virtual const char* what() const noexcept;

(since C++11)
(constexpr since C++26)

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

#include <iostream>
#include <typeinfo>
 
struct Foo { virtual ~Foo() {} };
struct Bar { virtual ~Bar() { std::cout << "~Bar\n"; } };
struct Pub : Bar { ~Pub() override { std::cout << "~Pub\n"; } };
 
int main()
{
    Pub pub;
    try
    {
        [[maybe_unused]]
        Bar& r1 = dynamic_cast<Bar&>(pub); // OK, upcast
 
        [[maybe_unused]]
        Foo& r2 = dynamic_cast<Foo&>(pub); // throws
    }
    catch (const std::bad_cast& e)
    {
        std::cout << "e.what(): " << e.what() << '\n';
    }
}

Possible output:

e.what(): std::bad_cast
~Pub
~Bar

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