Double pointer & Inheritance

[Prota]

Hi!

I am making a project about doublepointers and inheritance. Have some small issues that should not be difficult to resolve, but I just cant get a grip of it.

The task is to add two types of vehicles that have some of the same characteristics but not all. I'm using a dynamic allocated array that is declared as "Vehicle ** vehicles" to store all vehicles. This is a pointer that points to another pointer and this together with inheritance immediately becomes complicated (for me).

- My questions now is how I'm going to just show all the cars and not all vehicles.?

- It should also be possible that, from a vehicle, find out if it contains a certain character combinations in number and * is used to "fill" the positions of the registration number as we do not know the contents of (for example to search for all vehicles with registration begins at A and the last digits is 19 out of character sequence A *** 19.

I have 5 cpp-files and 4 h-files but I only show some of it, and if that's not enough for you to help me, then I can post more of my code and maybe all if that's necessary.

This is when I add a Car.

void VehicleManager::addCar(string brand, string age, string regNr, string price, string fuel, string size)
{
    if (this->count == this->capacity)
    {
        Vehicle **temp = new Vehicle*[this->capacity + 5];
        for (int i=0; i<capacity; i++)
        {
            temp[i] = this->vehicles[i];
        }
        delete [] this->vehicles;
        capacity += 5;
        this->vehicles = temp;
    }
    this->vehicles[this->count] = new Car(brand, age, regNr, price, fuel, size);
    this->count++;
}

This is when i show all the Vehicles

void VehicleManager::showAll()
{
    for(int i=0; i<this->count; i++)
    {
        cout <<this->vehicles[i]->getBrand() <<'\t' <<this->vehicles[i]->getRegNr()<< endl;
    }
}

[kunal kislay]

you are makin the object of derived class (car) using base class(vehicle) pointer.. thats correct..

but there should be a pure virtual funtion showType or show in base class which should be overridden in every derived class.

now when u call the show function it will autometically call ur derived class function and will display only what u require.

[Prota]

you are makin the object of derived class (car) using base class(vehicle) pointer.. thats correct..

but there should be a pure virtual funtion showType or show in base class which should be overridden in every derived class.

now when u call the show function it will autometically call ur derived class function and will display only what u require.

Okey, I understand what you mean, but if I do that I'll get an abstract class, and you can't instantiate an abstract class (Vehicle.h).

[kunal kislay]

do you need the instantiation of base class in your case.

use the pointer of base class to instantiate derived one..

and i think vehicle should be an abstract class...

//it should be like
vehicle *vech = new Car();

and if you still want to instantiate vehicle dont make the functions pure virtual insteed keep it virtual only
this way ur vehicle class wont be abstract..

[Prota]

do you need the instantiation of base class in your case.

use the pointer of base class to instantiate derived one..

and i think vehicle should be an abstract class...

//it should be like
vehicle *vech = new Car();

and if you still want to instantiate vehicle dont make the functions pure virtual insteed keep it virtual only
this way ur vehicle class wont be abstract..

I think i need the instanttiation of base class and if I make the functions only virtual I'll get LINK-errors.

[kunal kislay]

try it at least i think you wont get link errors

give ur virtual function a definition

if it dosent find its derived class definition then it will autometically call ur base definition..

[Prota]

try it at least i think you wont get link errors

give ur virtual function a definition

if it dosent find its derived class definition then it will autometically call ur base definition..

Okey, I've mad the functions virtual, but I dont know how to move on. What should i write for code to execute? How and from where to call it?

Maybe I should show my whole program?

[kunal kislay]

Okey, I've mad the functions virtual, but I dont know how to move on. What should i write for code to execute? How and from where to call it?

Maybe I should show my whole program?

sorry for the delay i was offline..

first u should know how virtual function works...

class vehicle
{

virtual void showType(); // only virtual in this case u can instanciate vehicle
{
           // you can have definition here
}
//or
virtual void showType() = 0;// this is pure virtual u cant instanciate vehicle now , and every derived class form vehicle has to override this function. there cannot be any definition here now. its the contract that derived class will use me as they want 
};

class Car : public vehicle
{
       void showType()
       {
            // u  can have definition here.. if showType() is virtual in base class this function will override base class definition. 
       }
           //if u do not write this function here and showType is only virtual in base class then base class definition will be called.
};

if you still have prob then show me ur code ill help

[Prota]

I wanna thank kunal kislay for helping me to show only one type of vehicles and many other things.

If nobody else can help me with the "registration number" I mark it as solved.