C-style cast suceeds whereas static_cast reports error

[miteshpandey]

I am using Visual Studio 2005:

The following code fails:

using namespace NepwareGames::MainApplication;

CApplicationCallback *pWin = static_cast<CApplicationCallback *>(new CWindow);

The error reported is

1>j:\nepwaregames\nepwaregames\nepwaregames.cpp(28) : error C2243: 'static_cast' : conversion from 'NepwareGames::MainApplication::CWindow *' to 'NepwareGames::MainApplication::CApplicationCallback *' exists, but is inaccessible

However the C-style cast works fine and the program executes as expected.

The following are the declaration of the classes:

namespace NepwareGames
{
	namespace MainApplication
	{
		class CApplicationCallback
		{
		public:
			// pure virtual functions
			virtual ~CApplicationCallback(void)= 0 {}
			virtual bool CreateEx(DWORD dwExStyle, LPCTSTR lpszClass, LPCTSTR lpszName, DWORD dwStyle,
									int x, int y, int nWidth, int nHeight, HWND hParent,
									HMENU hMenu, HINSTANCE hInst) = 0;
			virtual WPARAM MessageLoop(void) = 0;
			virtual BOOL ShowWindow(int nCmdShow) const = 0;
			virtual BOOL UpdateWindow(void) const = 0;
		};

		class CApplication
		{
		public:
			static CApplication * Create (CApplicationCallback *par);
		};
	}
}

namespace NepwareGames
{
	namespace MainApplication
	{
		class CWindow : CApplicationCallback
		{
		private:
			CApplication *m_CApplication;
		private:
			virtual void OnDraw(HDC hDC){}
			virtual void OnKeyDown(WPARAM wParam, LPARAM lParam);
			virtual LRESULT WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
			static LRESULT CALLBACK WindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
			virtual void GetWndClassEx(WNDCLASSEX & wc);
		public:
			HWND  m_hWnd;

			CWindow(void) : m_hWnd(NULL) {}
			~CWindow(void) {}
			virtual bool CreateEx(DWORD dwExStyle, LPCTSTR lpszClass, LPCTSTR lpszName, DWORD dwStyle,
									int x, int y, int nWidth, int nHeight, HWND hParent,
									HMENU hMenu, HINSTANCE hInst);
			bool RegisterClass(LPCTSTR lpszClass, HINSTANCE hInst);
			virtual WPARAM MessageLoop(void);
			virtual BOOL ShowWindow(int nCmdShow) const
			{
				return ::ShowWindow(m_hWnd, nCmdShow);
			}
			virtual BOOL UpdateWindow(void) const
			{
				return ::UpdateWindow(m_hWnd);
			}
		};
	}
}

Please help

[Yves M]

I may be missing something, but why do you even need a cast? CWindow is a derived class of CApplicationCallback so you don't need a cast to assign a derived pointer to a base pointer.

[miteshpandey]

Hi Yves,

Earlier I didn't use any casts. While not using any cast it gives the following error:

1>j:\nepwaregames\nepwaregames\nepwaregames.cpp(28) : error C2243: 'type cast' : conversion from 'NepwareGames::MainApplication::CWindow *' to 'NepwareGames::MainApplication::CApplicationCallback *' exists, but is inaccessible

The "inaccessible" thing is very puzzling. Default constructors are available for the both. Any ideas?

[Mybowlcut]

Apparently, class inheritance in C++ is private by default... can you spot the error in your code? I found this out by searching - *

[NMTop40]

I may be missing something, but why do you even need a cast? CWindow is a derived class of CApplicationCallback so you don't need a cast to assign a derived pointer to a base pointer.

Yes you missed something. His inheritance is private.

Try making the inheritance public thus:

class CWindow : public CApplicationCallback
{
// etc.
};

[Yves M]

Ah, yes

[miteshpandey]

Thanks Mybowlcut.

Gosh!!! I spent half an hour with this.

[Mybowlcut]

Haha no probs.. thanks for helping me out all those times! Feels great to help someone smarter than me, even if NMTop40 was only seconds away haha.