Class Templates question

This is a discussion on Class Templates question within the C++ Programming forums, part of the General Programming Boards category; Hi, I am trying to use a template for my classes, eg: Code: template<class VEHICLE> class SportsCar { //data members/functions ...

  1. #1
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    Class Templates question

    Hi,

    I am trying to use a template for my classes, eg:

    Code:
    template<class VEHICLE>
    class SportsCar
    {
    //data members/functions
    }
    I am eventually aiming to hold all the objects within a single linked list.

    My question though is that my classes whilst having the same member functions, they also have different data members.

    Is this a problem? The tutorials I have read show the use of Templates, but the data members are always the same, unlike mine.

    Perhaps I should declare all the different data members used by the separate inherited classes within the base class?

    Any advice is appreciated.

    Thanks!

  2. #2
    C++ Witch laserlight's Avatar
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    Perhaps you should describe what is the problem that you are trying to solve before jumping into the use of templates.
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    Code:
    class Vehicle
    {
    
    };
    
    class Car : public Vehicle
    {
    int MPG;
    int NoOfDoors;
    }
    
    class Motorbike : public : Vehicle
    {
    	int MPG;
    };
    In the code above , the base class is Vehicle.

    The two inherited classes have different data members.

    I want to use a Template (in the hope of storing the different objects within a single linked list).

    Such as:

    Code:
    template<class VEHICLE>
    class Vehicle
    {
    
    };
    
    template<class VEHICLE>
    class Car : public Vehicle
    {
    int MPG;
    int NoOfDoors;
    }
    
    template<class VEHICLE>
    class Motorbike : public : Vehicle
    {
    	int MPG;
    };
    I'm not saying I yet have a problem, I am wondering if having different data members in different classes stops you using a Template for all of the classes.

  4. #4
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by Swerve
    I want to use a Template (in the hope of storing the different objects within a single linked list).
    Your motivation to turn your classes into template classes seems strange: it sounds like you want to use a std::list<Vehicle*>, std::list<std::tr1::shared_ptr<Vehicle> > or boost::ptr_list<Vehicle> instead of involving templates.

    Quote Originally Posted by Swerve
    I'm not saying I yet have a problem, I am wondering if having different data members in different classes stops you using a Template for all of the classes.
    No, it does not.
    Last edited by laserlight; 03-29-2009 at 10:32 AM.
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    Thanks laserlight

  6. #6
    Cat without Hat CornedBee's Avatar
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    That would be std::list<std::tr1::shared_ptr<Vehicle> >
    All the buzzt!
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  7. #7
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by CornedBee
    That would be std::list<std::tr1::shared_ptr<Vehicle> >
    Yes, and corrected accordingly.
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    Thanks very much

    Code:
    std::list<std::tr1::shared_ptr<Vehicle> >
    I read this to mean there should be a shared pointer for the entire Vehicle type, and this pointer will point to all the objects within the list, yes?

  9. #9
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by Swerve View Post
    Thanks very much

    Code:
    std::list<std::tr1::shared_ptr<Vehicle> >
    I read this to mean there should be a shared pointer for the entire Vehicle type, and this pointer will point to all the objects within the list, yes?
    Not as such. shared_ptr is a "smart pointer" type that handles garbage-collection-type things for you (i.e., if all the shared_ptr's pointing to an object go out of scope, the object is deleted). But each pointer points to one object, and you have a list full of them.

    You don't need anything that fancy to do the basic sort of thing you're trying to do, if you don't want it. A plain old Vehicle* can hold a pointer to all its derived types, without any nonsense about templates or the like.

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