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Pure Virtual Functions. beginner help sought.

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Join Date: Mar 2009

Posts: 31

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Carrots

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Pure Virtual Functions. beginner help sought.

May 30th, 2009

Hi,

Hoping someone can tel me where I'm going wrong, or what I should do.

I'm trying to use some pure virtual functions on some polymorphic classess but am unsure how to do it correctly.

Hiopefully this code will explain it a bit better:

vehicle.h :

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
using namespace std;
 
class Vehicle
{
public:	
	Vehicle(int publicmpg = 0); 
 
protected:
 
	int protectedmpg;  
};
 
Vehicle::Vehicle(int publicmpg) 
{
	protectedmpg = publicmpg; 	
}
 
/////////////////////////////////
 
class VectorClass
{
public:
 
	//Declaring pure virtual function here causing Vehicle to become the ABC
	virtual void AddACar() = 0; 
 
protected:
 
};
 
/////////////////////////////////
 
class SportsCar : public Vehicle
{
public:
	SportsCar(int publicsixspeed = 0, int publicmpg = 0);
 
	//pure virtual member function for SportsCar
	void AddACar()
	{
		cout << "Inside myfunc() for SportsCar objects" << endl;
	} 
 
protected:
	int protectedsixspeed;
};
 
SportsCar::SportsCar(int publicsixspeed, int publicmpg) : Vehicle(publicmpg) 
{
	protectedsixspeed = publicsixspeed;
}
using namespace std;

class Vehicle
{
public:	
	Vehicle(int publicmpg = 0); 

protected:

	int protectedmpg;  
};

Vehicle::Vehicle(int publicmpg) 
{
	protectedmpg = publicmpg; 	
}

/////////////////////////////////

class VectorClass
{
public:

	//Declaring pure virtual function here causing Vehicle to become the ABC
	virtual void AddACar() = 0; 

protected:

};

/////////////////////////////////

class SportsCar : public Vehicle
{
public:
	SportsCar(int publicsixspeed = 0, int publicmpg = 0);

	//pure virtual member function for SportsCar
	void AddACar()
	{
		cout << "Inside myfunc() for SportsCar objects" << endl;
	} 

protected:
	int protectedsixspeed;
};

SportsCar::SportsCar(int publicsixspeed, int publicmpg) : Vehicle(publicmpg) 
{
	protectedsixspeed = publicsixspeed;
}

main.cpp :

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 C++ Syntax (Toggle Plain Text) 
#include <iostream>
#include <vector>
#include "Vehicle.h"
 
using namespace std;
 
int main()
{
	vector<Vehicle*> vectorname;
 
	int publicmpg = 11;
	int publicsixspeed = 22;
 
	SportsCar node(publicmpg, publicsixspeed);
 
	SportsCar *ptrToSportsCar;
 
	ptrToSportsCar = &node;
 
	vectorname.push_back( ptrToSportsCar );
 
	cout << "past push" << endl;
 
 
	vectorname[0]->AddACar(); 
 
 
	cout << "Past myfunc() call " << endl;
 
	system ("PAUSE");
	return 0;
}
#include <iostream>
#include <vector>
#include "Vehicle.h"

using namespace std;

int main()
{
	vector<Vehicle*> vectorname;

	int publicmpg = 11;
	int publicsixspeed = 22;

	SportsCar node(publicmpg, publicsixspeed);

	SportsCar *ptrToSportsCar;

	ptrToSportsCar = &node;

	vectorname.push_back( ptrToSportsCar );

	cout << "past push" << endl;


	vectorname[0]->AddACar(); 
	

	cout << "Past myfunc() call " << endl;

	system ("PAUSE");
	return 0;
}

Visual Studio reports:

•

'DeleteACar' : is not a member of 'Vehicle'

I'm going to use DeleteACar() to delete nodes from the Vector by passing which node as an argument, but before I attempt to write the function, I'm stuck as how to correctly configure a pure virtual function.

Any advice or advice is most appreciated.

Thanks!

Carrots.

Last edited by Carrots; May 30th, 2009 at 6:38 pm.

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Join Date: Nov 2008

Posts: 32

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Ahmed_I

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Re: Pure Virtual Functions. beginner help sought.

May 30th, 2009

in line 33 you should inherit from VectorClass to use the virtual method AddACar().
i just wanted to warn cuz the method AddACar() u used in main
isn't the virtual function that u declared in VectorClass.

Secondly i dont see any member function or attributes u declared named DeleteACar from where did the compiler get it??? plz tell the line that the error occured in.

Last edited by Ahmed_I; May 30th, 2009 at 7:09 pm.

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Join Date: Mar 2009

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Carrots

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Re: Pure Virtual Functions. beginner help sought.

May 30th, 2009

Thanks very much Ahmed !!

Where am I going wrong here?

I've tried:

class SportsCar : public VectorClass

class SportsCar : public Vehicle, public VectorClass

and

class SportsCar : public VectorClass, public Vehicle

None seem to work, where am I going wrong?

EDIT - Thanks Ahmed, just seen your edit and just getting my head around it. I haven't added any functionality to the function apart from the cout as I wanted to get a simplem function working before creating it fully.

Last edited by Carrots; May 30th, 2009 at 7:20 pm.

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Join Date: Nov 2008

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Ahmed_I

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Re: Pure Virtual Functions. beginner help sought.

May 30th, 2009

please could u tell me more about your problem do u want to solve the compiler's error or do u want to know how to configure a pure virtual function?

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Carrots

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Re: Pure Virtual Functions. beginner help sought.

May 30th, 2009

Solve the compiler's error for sure, that would be great.

Thanks very much, your taking the time to help me out is most apreciated 100%!

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Join Date: Nov 2008

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Ahmed_I

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Re: Pure Virtual Functions. beginner help sought.

May 30th, 2009

ok the compiler's error is

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DeleteACar' : is not a member of 'Vehicle'

and in your code i dont see any data or function named DeleteACar
so could u please tell check your code for DeleteACar.

But i think that u declared a vector with type Vehicle* and u pushed a pointer with type Sportscar .
when u say

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vectorname[0]->AddACar();

it means that u call AddACar() of the vehicle class which vehicle class hasnt this method .

So the solution is let the vehicle class be derived from VectorClass and implement AddACar() method for the vehicle class.
Your problem is in Polymorphism .
I hope that this is the solution for your problem.

Last edited by Ahmed_I; May 30th, 2009 at 8:05 pm.

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JugglerDrummer JugglerDrummer is offline

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Re: Pure Virtual Functions. beginner help sought.

May 30th, 2009

AddAcar should be a method of the vector, and probably deleteacar too judging by their names. SportsCar should inherit only from vehicle. The virtual function should be declared in vehicle (don't need =0; after function declaration

) and then overriden in sportscar.

92% of all statistics are made up on the spot.

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Join Date: Mar 2009

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Carrots

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Re: Pure Virtual Functions. beginner help sought.

May 30th, 2009

Noticing the 'solved threads' username tag, I can now say this thread is fully solved aswell!

Thank you so much, the classes are now fully working.

This is a great forum.

Here are the working classes now.

Using the VectorClass as the Interface makes everything flow down through the inherited classes nicely.

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
using namespace std;
 
 
class VectorClass
{
public:
 
	//Declaring pure virtual function here causing VectorClass to become an A.B.C.
	virtual void DeleteACar() = 0; 
 
protected:
 
};
 
/////////////////////////////////
 
 
class Vehicle : public VectorClass
{
public:	
	Vehicle(int publicmpg = 0); 
 
protected:
 
	int protectedmpg;  
};
 
Vehicle::Vehicle(int publicmpg) 
{
	protectedmpg = publicmpg; 	
}
 
/////////////////////////////////
 
 
 
/////////////////////////////////
 
//class SportsCar : public Vehicle
class SportsCar : public Vehicle
{
public:
	SportsCar(int publicsixspeed = 0, int publicmpg = 0);
 
	//pure virtual member function for SportsCar
	void DeleteACar()
	{
		cout << "Inside DeleteACar() for SportsCar objects" << endl;
	} 
 
protected:
	int protectedsixspeed;
};
 
SportsCar::SportsCar(int publicsixspeed, int publicmpg) : Vehicle(publicmpg) 
{
	protectedsixspeed = publicsixspeed;
}
 
 
//create the virtual function
 
//void DeleteACar(pointer to car or location within vector[])
void DeleteACar()
{
 
//	int x = vectorsize();
 
	cout << "Vector size is : "<< size() << endl;
 
	//for(int a = 0;a< vector size();a++)
 
	//{
	//	if vectorname[a] = match
 
	//	{
	//		delete vectorname[a];  
	//		break;
	//	}
	//}
 
}
using namespace std;


class VectorClass
{
public:

	//Declaring pure virtual function here causing VectorClass to become an A.B.C.
	virtual void DeleteACar() = 0; 

protected:

};

/////////////////////////////////


class Vehicle : public VectorClass
{
public:	
	Vehicle(int publicmpg = 0); 

protected:

	int protectedmpg;  
};

Vehicle::Vehicle(int publicmpg) 
{
	protectedmpg = publicmpg; 	
}

/////////////////////////////////



/////////////////////////////////

//class SportsCar : public Vehicle
class SportsCar : public Vehicle
{
public:
	SportsCar(int publicsixspeed = 0, int publicmpg = 0);

	//pure virtual member function for SportsCar
	void DeleteACar()
	{
		cout << "Inside DeleteACar() for SportsCar objects" << endl;
	} 

protected:
	int protectedsixspeed;
};

SportsCar::SportsCar(int publicsixspeed, int publicmpg) : Vehicle(publicmpg) 
{
	protectedsixspeed = publicsixspeed;
}


//create the virtual function

//void DeleteACar(pointer to car or location within vector[])
void DeleteACar()
{

//	int x = vectorsize();

	cout << "Vector size is : "<< size() << endl;
	
	//for(int a = 0;a< vector size();a++)

	//{
	//	if vectorname[a] = match

	//	{
	//		delete vectorname[a];  
	//		break;
	//	}
	//}

}