Question

When I write my try/catch blocks I always throw objects by value and catch by reference. I also apply the rule that the most derived classes must come first.

Today I tried to catch BY VALUE violating this main rule. The code below executes without any problem and prints "A4".

Question: what type of CCA argument is passed to the exception handler that executes? The original object thrown is CCB passed by value to a CCA object: is this an example of memory slicing problem or somekind of corruption i.e. the object CCA cannot be totally trusted?

Regards

AFG

  class CCA{
        int m_value;
  public:
        CCA( int value ) : m_value( value ){}            
  };

  class CCB : public CCA{
  public: 
        CCB( int value ): CCA( value ){}
  };


  main(){     
        try{
              throw CCB(4);
        }catch( CCA a ){
              std::cout << " A:" << a.value() << std::endl; 
              // this is the catch clause that executes
        }catch( CCB b ){
           std::cout << " B:" << b.value() << std::endl;
        }     
 }

Answer 1

This is slicing: The inability of the base copy constructor to discriminate an argument of the genuinely same type from one of a derived class type:

struct Base {
  Base(Base const &);  // must accept any derived class
};