bad_cast exception

Article
08/03/2021

The bad_cast exception is thrown by the dynamic_cast operator as the result of a failed cast to a reference type.

Syntax

catch (bad_cast)
   statement

Remarks

The interface for bad_cast is:

class bad_cast : public exception

The following code contains an example of a failed dynamic_cast that throws the bad_cast exception.

// expre_bad_cast_Exception.cpp
// compile with: /EHsc /GR
#include <typeinfo>
#include <iostream>

class Shape {
public:
   virtual void virtualfunc() const {}
};

class Circle: public Shape {
public:
   virtual void virtualfunc() const {}
};

using namespace std;
int main() {
   Shape shape_instance;
   Shape& ref_shape = shape_instance;
   try {
      Circle& ref_circle = dynamic_cast<Circle&>(ref_shape);
   }
   catch (bad_cast b) {
      cout << "Caught: " << b.what();
   }
}

The exception is thrown because the object being cast (a Shape) isn't derived from the specified cast type (Circle). To avoid the exception, add these declarations to main:

Circle circle_instance;
Circle& ref_circle = circle_instance;

Then reverse the sense of the cast in the try block as follows:

Shape& ref_shape = dynamic_cast<Shape&>(ref_circle);

Members

Constructors

Constructor	Description
bad_cast	The constructor for objects of type `bad_cast`.

Functions

Function	Description
what	TBD

Operators

Operator	Description
operator=	An assignment operator that assigns one `bad_cast` object to another.

bad_cast

The constructor for objects of type bad_cast.

bad_cast(const char * _Message = "bad cast");
bad_cast(const bad_cast &);

operator=

An assignment operator that assigns one bad_cast object to another.

bad_cast& operator=(const bad_cast&) noexcept;

what

const char* what() const noexcept override;