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How can I call the member function of the derived class

Posted on 2006-11-10
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Last Modified: 2010-04-01
Hi Experts,

In the following code, xx->test(bb); calls the member function from the base class.  How can I change the code to get the derived class's member function.

I want the output to show that it is 'In derived' when I call the member function of X

Thanks,


#include <string>
#include <iostream>
using namespace std;

class A
{
public:
      A(){};
      void printPlace(){cout << "In super" << endl;};

};

      
class B: public A
{
public:
      void printPlace(){cout << "In derived" << endl;};

};


class X
{

public:

      void test(A *a){ a->printPlace();};

};

void main () {


      B *bb = new B();
      A *aa = new A();
      bb->printPlace();
      aa->printPlace();


                X *xx = new X();
      xx->test(bb);

}
0
Comment
Question by:ambuli
2 Comments
 

Author Comment

by:ambuli
ID: 17920131
Declaring

class A
{
public:
     A(){};
     virtual void printPlace(){cout << "In super" << endl;};

};


solved the problem.  But, Why?  

Thanks,
0
 
LVL 86

Accepted Solution

by:
jkr earned 300 total points
ID: 17920145
Because by using the 'virtual' specfier, you tell the compileer that you expect the function to be redefined in derived classes. When you refer to a derived class object using a pointer or a reference to the base class, you can call a virtual function for that object and execute the derived class's version of the function.
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