How do one throw polymorphically?, C/C++ Programming

How do one throw polymorphically?              

A: Sometimes people write code such as:

class MyExceptionBase { };

class MyExceptionDerived : public MyExceptionBase { };

void f(MyExceptionBase& e)

{

// ... throw e;

}

void g()

{

MyExceptionDerived e;

try {

f(e);

}

catch (MyExceptionDerived& e) {

...code to handle MyExceptionDerived...

}

catch (...) {

...code to handle other exceptions...

}

}

If you attempt this, you might be astounded at run-time while your catch (...) clause is entered, & not your catch (MyExceptionDerived&) clause. It happens because you didn't throw polymorphically. The statement throw e , in function f(); throws an object  along with the same type as the static type of the expression e. In other terms, it throws an example of MyExceptionBase. The throw statement acts as-if the thrown object is copied, as opposed to developing a "virtual copy".

Luckily it's comparatively easy to correct:

class MyExceptionBase {

public:

virtual void raise();

};

void MyExceptionBase::raise()

{ throw *this; }

class MyExceptionDerived : public MyExceptionBase {

public:

virtual void raise();

};

 

void MyExceptionDerived::raise()

{ throw *this; }

void f(MyExceptionBase& e)

{

// ... e.raise();

}

void g()

{

MyExceptionDerived e;

try {

f(e);

}

catch (MyExceptionDerived& e) {

...code to handle MyExceptionDerived...

}

catch (...) {

...code to handle other exceptions...

}

}

Note down that the throw statement has been moved in a virtual function. The statement e.raise() will show polymorphic behavior, as raise() is declared virtual & e was passed through reference. As before, the thrown object will be of static type of the argument in the throw statement, however in MyExceptionDerived::raise(), that static type is MyExceptionDerived not MyExceptionBase.

 

Posted Date: 3/19/2013 8:52:07 AM | Location : United States







Related Discussions:- How do one throw polymorphically?, Assignment Help, Ask Question on How do one throw polymorphically?, Get Answer, Expert's Help, How do one throw polymorphically? Discussions

Write discussion on How do one throw polymorphically?
Your posts are moderated
Related Questions
#an array that accept input and gives an output

define a class for student

Additional keywords in C++ Class     friend    virtual   inline private  public    protected     const this         new       delete   operator The actual use and expl

within 2 mins give me answer pllzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz

Write a program that finds the minimum total number of shelves, including the initial one required for this loading process.

Two kinds of line detection are implemented in OpenCV, the Hough Transform and the probabilistic Hough transform. Assume that there are n feature points in an image and that it tak

C program to string compression: Write a program to define a sting and all operations on string. void main()                                 {

What are  Id e n t i f ie rs a n d C o n s t a n ts in C++? Id e n t i f ie r a n d C o n s t a n t : I d e n t i f ie r

Make a list of functions that are standard in C++. You must include each of the following for each function: Name of function Its parameters Data type it returns

Construct a console program to manage the booking of a Hotel room.