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