std::bad_cast(3)

NAME
std::bad_cast - std::bad_cast

Synopsis
   Defined in header <typeinfo>
   class bad_cast : public std::exception;
   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.
   std-bad cast-inheritance.svg
                        Inheritance diagram

Member functions
   constructor constructs a new bad_cast object
                 (public member function)
   operator= replaces the bad_cast object
                 (public member function)
   what returns the explanatory string
                 (public member function) std::bad_cast::bad_cast
   bad_cast() throw(); (until C++11)
   bad_cast() noexcept; (1) (since C++11)
   bad_cast( const bad_cast& other ) throw(); (2) (until C++11)
   bad_cast( const bad_cast& other ) noexcept; (since C++11)
   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)
   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)
   Returns the explanatory string.

Parameters
   (none)

Return value
   Pointer to a 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.

Notes
   Implementations are allowed but not required to override what(). Inherited from std::exception

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

Example
// Run this code
 #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