Correct model? Virtual functions.

This is a discussion on Correct model? Virtual functions. within the C++ Programming forums, part of the General Programming Boards category; Hi, I would explain what I want to do, but I think that the code explains better. Basically, I need ...

  1. #1
    Registered User Mortissus's Avatar
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    Correct model? Virtual functions.

    Hi, I would explain what I want to do, but I think that the code explains better. Basically, I need that an initialization and finalization code are executed before (and after) different other functions (sorry, very bad explanation), here is the code:
    Code:
    #include <iostream>
    
    using namespace std;
    
    class A {
    public:
    		void action() {
    				cout << "Before update." << endl;
    				update();
    				cout <<	"After update." << endl;			
    		}
    
    		virtual void update() {
    				cout << "Updating class A." << endl;
    		}		
    };
    
    
    class B : public A {
    public:
    		void update() {
    				cout << "Updating class B." << endl;
    		}
    };
    
    
    class C : public A {
    public:
    		void update() {
    				cout << "Updating class C." << endl;
    		}
    };
    
    int main()
    {
    		C c;
    		B b;
    
    		b.action();
    		c.action();
    
    		return 0;
    }
    Is this code "portable" and "right"?

  2. #2
    Registered User
    Join Date
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    7,317
    >> Is this code "portable" and "right"?
    Yes.

    In fact, it is a recommended way of using polymorphism (see C++ Coding Standards Item #39). You would want to make update private or protected, though. Then what you are doing is exposing only the non-virtual action member function to users of the A hierarchy. Then you implement action() with virtual functions. Even if action() didn't have any other code than calling private or protected virtual methods, it would still make sense to do it that way.

    Don't forget to make A's destructor virtual. Also, a better example of usage might be this since it uses B and C polymorphically:
    Code:
    void DoWork(A& a)
    {
    	a.action();
    }
    
    int main()
    {
    	C c;
    	B b;
    
    	DoWork(b);
    	DoWork(c);
    
    	return 0;
    }
    Last edited by Daved; 06-25-2007 at 11:14 AM.

  3. #3
    Registered User Mortissus's Avatar
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    Thanks very much! =)

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