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my Inheritance errors or not?

my Inheritance errors or not?, my Inheritance errors or not?

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khunmk	30 Aug, 2008 - 12:13 PM Post #1
New D.I.C Head Joined: 30 Aug, 2008 Posts: 2	Hi all, I'm a beginner in C++. I got a problem with some of my codes. Like this CODE #include<iostream.h> class Base { public: void show() { //that will do my some works } }; class Inher1 { public: void show() { //this one also will do my some works } }; int main() { Inher1 hr1; //object of my Inher1 Base *ptr; ptr = &hr1; ptr->show(); //my problem is here... return 0; } My problem is on ptr->show(). why it always display the answer from the base class. cause of my function error? I'm beginner. Pls teach to me. what i'm wrong.
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KYA

30 Aug, 2008 - 01:20 PM

Post #2

#include <nerd.h>

Joined: 14 Sep, 2007
Posts: 4,205

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You have not set up inheritance and you created a pointer to the base class. Here is an example of what you may be trying to do:

cpp


#include<iostream.h>

class Base
{
     public:
         void show() {  //that will do my some works }
};

class Inher1 : public Base // inher derives from base class
{
     public:
         void show() {  //this one also will do my some works }
};

int main()
{
   Base* ptr = new Inher1(); //declare a new object, why not just make it an inher1 pointer
    //I would need to know your intentions here, for above

    ptr->show();      //my problem is here...
    delete ptr;
    return 0;
}

That's the general idea. Was this post helpful?

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JackOfAllTrades

30 Aug, 2008 - 05:21 PM

Post #3

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Joined: 23 Aug, 2008
Posts: 502

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Should make the show method virtual.

cpp

#include<iostream.h> 
 
class Base  
{  
      public:  
          virtual void show() { std::cout << "Show in Base" << std::endl; }  
};  
 
class Inher1 : public Base // inher derives from base class  
{  
     public:  
         virtual void show() {  std::cout << "Show in Inher1" << std::endl; }  
};  
  
int main()  
{  
   Base* ptr = new Inher1(); //declare a new object, why not just make it an inher1 pointer  
    //I would need to know your intentions here, for above  
  
   ptr->show();      //my problem is here...  
   delete ptr;  
   return 0;  
}

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KYA	30 Aug, 2008 - 05:46 PM Post #4
#include <nerd.h> Joined: 14 Sep, 2007 Posts: 4,205 Thanked 50 times Dream Kudos: 1150 My Contributions	Only the base class method needs to be virtual so that it knows to override with the inherited class method when called.
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khunmk	30 Aug, 2008 - 07:12 PM Post #5
New D.I.C Head Joined: 30 Aug, 2008 Posts: 2	Wooo ! Great.. all ! I can solve my problem with all your method. Than a million to you all. Sorry for I forgot this class Inher1 : public Base I want to ask again. I create a pointer to the Base. But I insert the address Hr1 to the pointer. Why it show the error.
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KYA	30 Aug, 2008 - 07:22 PM Post #6
#include <nerd.h> Joined: 14 Sep, 2007 Posts: 4,205 Thanked 50 times Dream Kudos: 1150 My Contributions	You need to create a 'new' object, not just assign memory address This post has been edited by KYA: 30 Aug, 2008 - 07:23 PM
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