C / C++ / MFC

4-Jul-07 12:00

I newbee to OO so ...

Is deriving a Class and Writting your own constructer for the base a way of accessing the bases private members ??

Christian Graus4-Jul-07 12:10

Christian Graus

4-Jul-07 12:10

Kind of - if a constructor sets the values, you can use it to set them. But, once they are set, you cannot access them, unless public methods are offered to do so ( often a class will offer methods to get, but not set some of the values )

Christian Graus - Microsoft MVP - C++

"I am working on a project that will convert a FORTRAN code to corresponding C++ code.I am not aware of FORTRAN syntax" ( spotted in the C++/CLI forum )

ForNow4-Jul-07 12:16

4-Jul-07 12:16

Meaning you the drived Class can access the private members only once durning initilization I guess to put total control on a data members can
add const to private ?????

Re: Accessing private members of a base Class [modified]

Rajkumar R4-Jul-07 18:32

Rajkumar R

4-Jul-07 18:32

No, private members can't be accessed even at initialization. The constructor you are refering may be public or protected. If your constructor is private then that constructor cannot be accessed from outside the class.

G Haranadh4-Jul-07 21:22

G Haranadh

4-Jul-07 21:22

Rajkumar_R wrote:
private members can't be accessed even at initialization.

Rajkumar_R wrote:
The constructor you are refering may be public or protected.

class myCls<br />
{<br />
private:<br />
    int x,y;<br />
public:<br />
    myCls()<br />
    {<br />
        x = 5100; //Initilization of private data.<br />
        y = 5660; //Initilization of private data. <br />
        ///???AM I WRONG DOING HERE IN PRIVATE SECTION???<br />
    }<br />
    void disp()<br />
    {<br />
        printf("x = %d;y = %d",x,y);<br />
    }<br />
};<br />
void main()<br />
{<br />
    class myCls obj;<br />
    obj.disp();<br />
}

-- modified at 10:46 Thursday 5th July, 2007

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David Crow5-Jul-07 3:01

David Crow

5-Jul-07 3:01

G Haranadh wrote:
please give a conclusion for private data members.

What exactly are you wanting to do with them?

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Rajkumar R8-Jul-07 23:19

Rajkumar R

8-Jul-07 23:19

Still, here constructor is accessed in main() because it is public.
constructor in turn accessed the private member. private member is not accessed in the main.

ForNow5-Jul-07 6:42

5-Jul-07 6:42

If I write my own constructer for the Base Class what Can I do/access/modify with it

thankx

Joe Woodbury5-Jul-07 10:14

5-Jul-07 10:14

If a base class has private members, a derived class (or any other for that matter) can access them only by using the friend keyword. Use it with caution, though (overuse of friend is a sign of a bad class designer.)

Anyone who thinks he has a better idea of what's good for people than people do is a swine.
- P.J. O'Rourke

ForNow5-Jul-07 11:30

5-Jul-07 11:30

Well normally if you write your own constructer in a derived class what can you do in it

Joe Woodbury5-Jul-07 12:00

5-Jul-07 12:00

The access rules apply to all members of a class. Your class should be designed so that the base class constructors and members would Get/Set the private member data within it's direct scope.

To be more clear; any method or data member defined in a class is accessible within that class, regardless of whether it's private, protected or public. Access modifiers control the visibility of methods to derived classes.

Thus a private data member in a base class is visible to methods in that base class. It is not visible, however, to any derived classes (unless friend is used.)

Anyone who thinks he has a better idea of what's good for people than people do is a swine.
- P.J. O'Rourke

ForNow5-Jul-07 13:22

5-Jul-07 13:22

The point I was making that to access private members of a base class all you have to do is write your own base contructer (maybe I am just thinking like a Hacker) but.... I am just trying to understand

Joe Woodbury5-Jul-07 13:31

5-Jul-07 13:31

Yes. You could do that, provide protected or public methods in the base class to that data or make your derived class a friend of the base class.

If this is a one time initialization and you don't want anyone but derived classes to set this data, make a protected constructor in the base class with the proper parameters and reference that in the constructor initialization list of the derived class.

Anyone who thinks he has a better idea of what's good for people than people do is a swine.
- P.J. O'Rourke

ForNow5-Jul-07 16:14

5-Jul-07 16:14

Do I really need to do any of that cann't I just write my own base class contructer since its a base class contructer it should be able to access anything in the base

Joe Woodbury5-Jul-07 16:19

5-Jul-07 16:19

yes

Anyone who thinks he has a better idea of what's good for people than people do is a swine.
- P.J. O'Rourke

ForNow5-Jul-07 16:25