| Topic: |
DEVELOP > c-Plus-Plus |
| User: |
"Vince" |
| Date: |
31 Jul 2005 03:48:54 AM |
| Object: |
forward declaration and templated class |
Hi,
I have a templated class implemented in one file called CDynWnd.h
and declared like this :
CDynWnd.h (declaration and implementation)
------------
template <class BASECLASS> class CDynWnd : public BASECLASS
{
// Construction
public:
CDynWnd(int nIDD);
CDynWnd(int nIDD, CWnd* pParent);
CDynWnd();
... and so on ...
}
Now I would like to declare a new class called CDynContextMenu,
so in the .h I declare it as shown below with a forward declaration
DynContextMenu.h
-----------------
#include "DynContextMenu.h" (Only declaration)
template <class BASECLASS> class CDynWnd;
class CDynContextMenu
{
public:
CDynContextMenu();
virtual ~CDynContextMenu();
virtual CMenu* GetPopupMenu( CDynWnd<BASECLASS>* editor );
protected:
CMenu m_menu;
};
DynContextMenu.cpp (implementation)
----------------
....
....
But when I compile I get this :
Compiling...
DynContextMenu.cpp
d:\developpement\borne_300705\dyncontextmenu.h(13) : error C2065:
'BASECLASS' : undeclared identifier
.
|
|
| User: "Jonathan Mcdougall" |
|
| Title: Re: forward declaration and templated class |
31 Jul 2005 04:08:05 AM |
|
|
Vince wrote:
Hi,
I have a templated class implemented in one file called CDynWnd.h
and declared like this :
CDynWnd.h (declaration and implementation)
------------
template <class BASECLASS> class CDynWnd : public BASECLASS
{
// Construction
public:
CDynWnd(int nIDD);
CDynWnd(int nIDD, CWnd* pParent);
CDynWnd();
... and so on ...
}
Now I would like to declare a new class called CDynContextMenu,
so in the .h I declare it as shown below with a forward declaration
DynContextMenu.h
-----------------
#include "DynContextMenu.h" (Only declaration)
template <class BASECLASS> class CDynWnd;
class CDynContextMenu
{
public:
CDynContextMenu();
virtual ~CDynContextMenu();
virtual CMenu* GetPopupMenu( CDynWnd<BASECLASS>* editor );
The name BASECLASS does not exists by itself. It is a template
parameter which must be obtained. You do that by making the class a
template class or (probably what you want) by making this member
function a template:
template <class BASECLASS>
CMenu *GetPopupMenu(CDynWnd<BASECLASS> *editor)
{
}
Two implications: GetPopupMenu() cannot be virtual anymore and you will
probably need to define the function inline.
Think about it: you want to pass a type to CDynWnd, but you don't have
that type. If you wanted for example and int:
CMenu *GetPopupMenu(CDynWnd<int> *editor)
{
}
but since you want any type, you need to use a template, hence
template <class BASECLASS>
CMenu *GetPopupMenu(CDynWnd<BASECLASS> *editor)
{
}
Note that you could use any name:
template <class T>
CMenu *GetPopupMenu(CDynWnd<T> *editor)
{
}
protected:
CMenu m_menu;
};
But when I compile I get this :
Compiling...
DynContextMenu.cpp
d:\developpement\borne_300705\dyncontextmenu.h(13) : error C2065:
'BASECLASS' : undeclared identifier
You should read a bit more about templates before continuing. It seems
there are some basic notions you don't get.
Jonathan
.
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