C / C++ / MFC

Re: How make a smart reference expose methods of basetype ?

20-Feb-07 23:05

I have written a reference class for one of my classes. It implements reference counting for that class and that's pretty much it. I have written a cast operator to the class type it references, but the compiler does not use that operator implicitly, so whenever i want to access the referenced object, i have to do an explicit cast (or call a method like getObject()). How can i prevent that ?

Here some code to illustrate my problem :

class MyClassReference;

class MyClass
{
public:
    void doStuff();                         //  do that thing you do
    static MyClassReference getInstance();  //  get an instance of the class, but wrapped in
                                            //  my custom reference-class

    ~MyClass();
private:
    friend class MyClassReference();

    MyClass();                              //  private, so you have to use getInstance();

    void addReference();
    void removeRererence();                 //  if (m_referenceCounter == 0) delete this;

    int m_referenceCounter;
};

class MyClassReference
{
public:
    MyClassReference(MyClass &object);  //  call addReference
    //  fancy copy-constructors and assignment-operators here
    operator MyClass &();               //  cast to contained object, not used implicitly

    ~MyClassReference();                //  call removeReference
};

This is just the principle, feel free to comment on it.

wbr

Brainley

Cedric Moonen20-Feb-07 23:17

Cedric Moonen

20-Feb-07 23:17

Your operator needs to return the reference to your class:

MyClass& operator& ();

Cédric Moonen
Software developer

Charting control [v1.1]

Re: How make a smart reference expose methods of basetype ? [modified]

Mr.Brainley20-Feb-07 23:54

Re: How make a smart reference expose methods of basetype ?

20-Feb-07 23:54

same error : doStuff() is not a member of MyClassReference.

-- modified at 6:00 Wednesday 21st February, 2007

Cedric Moonen21-Feb-07 0:12

Cedric Moonen

21-Feb-07 0:12

Show the code that is giving the error.

Cédric Moonen
Software developer

Charting control [v1.1]

Re: How make a smart reference expose methods of basetype ?

Mr.Brainley21-Feb-07 0:42

Re: How make a smart reference expose methods of basetype ?

21-Feb-07 0:42

MyClassReference ref = MyClass::getInstance();

ref.doStuff();    // C2039: 'doStuff' is not a member of 'MyClassReference'

He does not apply the cast implicitly. The following works :

((MyClass&)ref).doStuff();

The compiler told me though, that i have to declare the cast operator

operator class CNeighbour &();

in order for this to work. But he still does not apply the cast-operator implicitly.

Cedric Moonen21-Feb-07 0:54

Cedric Moonen

21-Feb-07 0:54

Of course, you are not using the operator at all ! So it is logical that it complains.
BTW, are you trying to do something similar as a smart pointer (but using references instead) ?

Cédric Moonen
Software developer

Charting control [v1.1]

Re: How make a smart reference expose methods of basetype ?

Mr.Brainley21-Feb-07 1:18

Re: How make a smart reference expose methods of basetype ?

21-Feb-07 1:18

1. Yes, it's not used. Thought it might be possible to use it implicitly, so the code looks better.
2. Yes. It actually is a smart pointer internally, but i tried to give it reference semantics and syntax. I need this for a synchronization problem. I have a list of references that is accessed from many threads. If one thread retrieves a reference from that list, and the list is cleared while it works on the reference, the reference remains valid until it goes out of scope (if it is a smart reference). This way i can minimize synchronization to the pure access on the list.

Maybe it would be better if i just overloaded the '->'-operator. It would have pointer-syntax then, but that would be ok i guess.

prasad_som21-Feb-07 1:12

21-Feb-07 1:12

Mr.Brainley wrote:
The compiler told me though, that i have to declare the cast operator

You need to apply that cast. Overloading operation MyClass doesn't mean that you can call members of MyClass using MyClassReference object. By doing this,you can cast MyClassReference class object for MyClass class.

Prasad
Notifier using ATL | Operator new[],delete[][^]

focus window

rushiraj.jhala20-Feb-07 22:46

20-Feb-07 22:46

hi,
I am new to vc++ , can any one tell me how to if window containg perticular view is focused or not.

I have one doc/view application in that in my CView class I have overloadedd onmouse active method now in that I want to check if the chid fram contaning that view is alredy active or not?

thanks in advance.
Rushiraj

prasad_som20-Feb-07 22:53

20-Feb-07 22:53

CWnd::GetFocus returns pointer to window having focus.

Prasad
Notifier using ATL | Operator new[],delete[][^]

rushiraj.jhala20-Feb-07 23:04

20-Feb-07 23:04

hi I have written this

int status = CView::OnMouseActivate(pDesktopWnd, nHitTest, message);
if(GetFocus()!=GetParent())
GetParentFrame()->SetFocus()->RedrawWindow();
return status;

what i want is it will not redraw window when foucs is on the same window and i clicked.

but in this code it always go in if condition.

Thanks ,
Rushiraj

prasad_som20-Feb-07 23:11

20-Feb-07 23:11

rushiraj.jhala wrote:
if(GetFocus()!=GetParent())

This should be like this,

if((*GetFocus())!=(*GetParent()))
{
 //your code
}

Prasad
Notifier using ATL | Operator new[],delete[][^]

rushiraj.jhala20-Feb-07 23:15

20-Feb-07 23:15

sorry,
it is not woriking for me.

prasad_som20-Feb-07 23:19

20-Feb-07 23:19

rushiraj.jhala wrote:
it is not woriking for me.

I told you the way to compare the windows.

What type of error it is givng. I could not understand your logic basically.

Prasad
Notifier using ATL | Operator new[],delete[][^]

rushiraj.jhala20-Feb-07 23:25

20-Feb-07 23:25

int CImageView::OnMouseActivate(CWnd* pDesktopWnd, UINT nHitTest, UINT message)
{
int status = CView::OnMouseActivate(pDesktopWnd, nHitTest, message);
if((*GetFocus())!=(*GetParent()))
GetParentFrame()->SetFocus()->RedrawWindow();
return status;
}

I have one Doc/view applivation in that i have one other dialog box also.
so when i click inside the view of my chid frame i want to check if this chid has foucs or not because if this frame has allready focus i dont need to redraw window other wise if dialog has foucs i have to set foucs the chid frame containing that view and redraw widnow.

for that in onmouseactive i wnat to check child frame is fouced or dialog box has foucs.

prasad_som20-Feb-07 23:51

20-Feb-07 23:51

rushiraj.jhala wrote:
so when i click inside the view of my chid frame i want to check if this chid has foucs or not

Whenever you click on a window, it will get focus automatically.

Prasad
Notifier using ATL | Operator new[],delete[][^]

rushiraj.jhala20-Feb-07 23:59

20-Feb-07 23:59

yes it will be

what i want is if child frame is focused and I click in client area of child i dont want to call GetParentFrame()->SetFocus()->RedrawWindow().

but in other case if dialog is focused and when i click on client area of child it will be focused but in addition i want to call GetParentFrame()->SetFocus()->RedrawWindow() function.

for that i want to know befour i have clicked is this child window is fouced or dialog.

prasad_som21-Feb-07 1:28