Re: [Dev-C++] protected and private in c++ classes

[Per W. <pw...@ia...>]

I wrote terse, but was actually correct:
"Private is only for methods of the class" as in: privately declared
member fields and methods may only be accessed by members of that class :)

I didn't say that only methods may use private. I meant that only methods
of that class may acccess any private fields, methods, constructors, ...

I don't think it's correct to say that methods are usually public. There
are just as large reasons to keep methods protected or private as there
are to keep variables protected or private.

I think you missed a bit about inherritance of access rights to protected
fields. The protected declarations will continue to be protected for
multiple generations, unless one of the inherritances stops it, i.e.

class A {
protected:
    int a;
};

class B : public A {
    // a still protected
};

class C : public B {
    // a still protected
};

class D : private C {
    // a now private because parent C is private!
};

class E : public D {
    // No longer access to field a, since class D
    // declared it's parent relation as "private".
};

/Per W

On Tue, 9 Mar 2004, Daniel Glenfield wrote:

> I don't think that is quite correct.
>
> Without getting too nerdy, private specifies that the member variable or
> method (methods are usually public, not private) can only be accessed by a
> method of that class, and cannot be accessed directly.
> So if I have a private member
> int EmployeeID;
> I cannot do
>
> MyObject.EmployeeID = 12345;
> Because it is private. What I need is a public method like this
>
> void SetEmployeeID(int Num)
> {
>     EmployeeID = Num;
> }
> Then I can do MyObject.SetEmployeeID(12345);
>
>
> Protected means the members are public to that class, but if a class is
> derived from it then they become private. e.g.
>
> class Person
> {
> protected:
> double DNASequence;
> }
>
> class Employee : public Person
> {
>     // class Employee now has
>     // private :         <<<< wrong

      // protected:            <<<< still protected, since parent
>     // double DNASequence;   <<< class was declared "public Person"
>
> }

 class Supervisor : private Employee
 {
      // class Supervisor also has PROTECTED
      // DNASequence, i.e.

     void clone(double newDNASequence) {
         // OK, since Supervisor is a descendant from Person, and
         // Empployee inherrited with public!
         // Supervisor Bhas access rights to DNASequence
         DNASequence = newDNASequence;
 }

 class MeanSupervisor : public Supervisor
 {
     void mutate(double amount) {
         // NOT ALLOWED, since Supervisor inherrited privately
         // from Employee.
         // MeanSupervisor does not have access rights to DNASequence
         DNASequence *= amount;
     }
 }
>
> Let me know if any of this sounds wrong.
>
> Daniel
>
>
> >From: Per Westermark <pw...@ia...>
> >To: studioartoni <stu...@li...>
> >CC: Dev...@li...
> >Subject: Re: [Dev-C++] protected and private in c++ classes
> >Date: Tue, 9 Mar 2004 11:15:18 +0100 (CET)
> >
> >Private is only for methods of the class.
> >
> >Protected are also available to all inherriting classes.
> >
> >/Per W
> >
> >On Tue, 9 Mar 2004, studioartoni wrote:
> >
> > > Excuse the question,
> > > but which is the difference between 'protected' and 'private' in c++
> >classes?
> > > Thank you.
> > >
> > >
> >
> >
> >
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