bad_cast Exception

 

The latest version of this topic can be found at bad_cast Exception.

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

catch (bad_cast)  
   statement  

The interface for bad_cast is:

class bad_cast : public exception {  
public:  
   bad_cast(const char * _Message = "bad cast");  
   bad_cast(const bad_cast &);  
   virtual ~bad_cast();  
};  

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.h>  
#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) is not 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);  

dynamic_cast Operator
Keywords
C++ Exception Handling

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