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std::bad_cast

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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.

cpp/error/exceptionstd-bad cast-inheritance.svg

Inheritance diagram

Contents

[edit] 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

(1)
bad_cast() throw();
(until C++11)
bad_cast() noexcept;
(since C++11)
(2)
bad_cast( const bad_cast& other ) throw();
(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

[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]

[edit] Example

#include <iostream>
#include <typeinfo>
 
struct Foo { virtual ~Foo() {} };
struct Bar { virtual ~Bar() {} };
 
int main()
{
    Bar b;
    try {
        Foo& f = dynamic_cast<Foo&>(b);
    } catch(const std::bad_cast& e)
    {
        std::cout << e.what() << '\n';
    }
}

Possible output:

Bad dynamic cast