dev-cpp-users

[Dev-C++] Subclass inside a class problem

[Brian B. <bcb...@ya...>]

Hi,
When trying to subclass an richedit control within a
class, I ran accross a problem. When I include a
subclass procedure in a class (the code shown below),
I get the error (Generated by Dev-C++): "aggregate
value used where an integer was expected", yet when I
include the subclass procedure outside the class, it
runs fine. How can I solve this?

class akorichedit{
private:
//...
WNDPROC wpOrigRichEditProc;
LRESULT CALLBACK RichEditSubclassProc(HWND hwnd, UINT
uMsg, WPARAM wParam, LPARAM lParam);
//...
public:
void create();
//...
};

void akorichedit::create(){
//... ERROR BELOW
wpOrigRichEditProc =(WNDPROC) SetWindowLong(
    (HWND)_hwnd,	// handle of window
    (int)GWL_WNDPROC,	// offset of value to set
  (LONG)RichEditSubclassProc
   );	// LINE 130
//... ERROR ABOVE
}

//...

LRESULT CALLBACK
akorichedit::RichEditSubclassProc(HWND hwnd, UINT
uMsg, WPARAM wParam, LPARAM lParam){
//...
}

Respectfully,
Brian

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Re: [Dev-C++] Subclass inside a class problem

[Elias P. <eli...@ao...>]

...
>
> class akorichedit{
> private:
> //...
> WNDPROC wpOrigRichEditProc;
> LRESULT CALLBACK RichEditSubclassProc(HWND hwnd, UINT
> uMsg, WPARAM wParam, LPARAM lParam);
> //...
> public:
> void create();
> //...
> };
>
...

I think callback functions have to be static. (I remember reading
something about this in one of the microsoft examples - but maybe i'm
wrong)

Elias Pschernig

Re: [Dev-C++] Subclass inside a class problem

[Michael P. <mdp...@ya...>]

You are not wrong Elias. All Callback functions must
be static. The windows calling procedure does not know
about the implicit 'this' pointer that is passed to
every non-static class member function.  With out the
'this' pointer, the appropriate instance of the class
can not be called.

Static functions do not have a this pointer and are
unaware of a specific class instance.  You must always
find a way to pass or store a pointer to your class if
you need it when a callback is fired. 




--- Elias Pschernig <eli...@ao...> wrote:
> ...
> >
> > class akorichedit{
> > private:
> > //...
> > WNDPROC wpOrigRichEditProc;
> > LRESULT CALLBACK RichEditSubclassProc(HWND hwnd,
> UINT
> > uMsg, WPARAM wParam, LPARAM lParam);
> > //...
> > public:
> > void create();
> > //...
> > };
> >
> ...
> 
> I think callback functions have to be static. (I
> remember reading
> something about this in one of the microsoft
> examples - but maybe i'm
> wrong)
> 
> Elias Pschernig
> 
> 
> _______________________________________________
> Dev-cpp-users mailing list
> Dev...@li...
>
http://lists.sourceforge.net/lists/listinfo/dev-cpp-users


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