C / C++ / MFC

12-Jul-07 22:48

Hi list,

I want to ask whether is it possible to have a pointer whose type can change according to the input. I want to make it clear waht I need by a little code below which is not possible to compile. I think there must be a very well known trick for this. Thanks in advance for your help.

switch( datatype )
{
case DT_INT8: char *myPntr = (char *)dataPntr
case DT_UINT8: unsigned char *myPntr = (unsigned char*)dataPntr;
case DT_INT16: short *myPntr = (short *)dataPntr;
}

dataPntr is a (void *).
how can I create such myPntr?

xonobo

Emmanouil12-Jul-07 23:05

Emmanouil

12-Jul-07 23:05

you just write: void * myPntr;

xonobo13-Jul-07 1:32

13-Jul-07 1:32

just read the reply of jhwurmbach below. That's my problem. void * do not help in that. but thanks...

jhwurmbach12-Jul-07 23:08

jhwurmbach

12-Jul-07 23:08

xonobo wrote:
want to ask whether is it possible to have a pointer whose type can change according to the input.

A void* can point to anything, but in turn it looses the information to what it is pointing.
You need to bundle this information with it.
In VB this is done using the VARIANT struct. That is a struct holding a type marker and a piece of memory.
Via a union, all datatypes are 'layered" above each other, using the same memory.

Failure is not an option - it's built right in.

xonobo13-Jul-07 1:34

13-Jul-07 1:34

Thanks a lot for your reply and ask: anyone knows a solution for C/C++?

jhwurmbach13-Jul-07 1:40

jhwurmbach

13-Jul-07 1:40

You don't tell enough to get a solution to your problem.
What are you trying to accomplish and why can't this be solved in another way?
Does the (Microsoft specific) _variant_t help you?

Failure is not an option - it's built right in.

xonobo13-Jul-07 4:19

13-Jul-07 4:19

Thamks for your help. I thought VARIANT is only available in VB that's why I asked more. Now I will check _variant_t. Thanks again.

David Crow13-Jul-07 4:25

David Crow

13-Jul-07 4:25

xonobo wrote:
I thought VARIANT is only available in VB...

It's definitely not limited to VB.

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

maximizing window in MFC application

Stephen Hewitt15-Jul-07 13:55

Stephen Hewitt

15-Jul-07 13:55

Try http://www.boost.org/doc/html/variant.html[^] and http://www.boost.org/doc/html/any.html[^].

Steve

minkowski12-Jul-07 22:18

minkowski

12-Jul-07 22:18

Hi,

I have a MFC application and wish to change the way the application behaves when a user maximises the main window frame. I understand that I need to add a virtual function to the document class that inherits from the CDocument class. However, I am not sure what the name of the function is that is used when maximising the window. If you can tell me, that would be great.

Thanks !

Sam_c12-Jul-07 22:38

Sam_c

12-Jul-07 22:38

the OnSize function takes UINT which identifies the minimise or maximise request.
that how ever is in MainFrm and View not Doc

example of an action based on minimised action.

void CMainFrame::OnSize(UINT nType, int cx, int cy)<br />
{<br />
	if(nType == SIZE_MINIMIZED)<br />
	{<br />
		ShowWindow(SW_HIDE);<br />
	}<br />
	else<br />
	{<br />
		CFrameWnd::OnSize(nType, cx, cy);<br />
	}<br />
}

hope that helps.
if im wrong about the document OnSize let me know please Smile | :)

minkowski12-Jul-07 23:17

minkowski

12-Jul-07 23:17

Hi ya,

Thanks for your post. I actually found this

<br />
<br />
void CMainFrame::OnGetMinMaxInfo(MINMAXINFO FAR* lpMMI) <br />
{<br />
	// kiran.<br />
	static const CPoint point0 = CPoint(0, 0);<br />
	if(m_PageSize != point0)<br />
	{<br />
		const long my = lpMMI -> ptMaxSize.y;<br />
		const long ty = lpMMI -> ptMaxTrackSize.y;<br />
		lpMMI -> ptMaxSize = m_PageSize;	<br />
		lpMMI -> ptMaxTrackSize = m_PageSize;<br />
		lpMMI -> ptMaxSize.y = my;<br />
		lpMMI -> ptMaxTrackSize.y = ty;<br />
	}<br />
<br />
	CFrameWnd::OnGetMinMaxInfo(lpMMI);<br />
}<br />
<br />

in my code and put a break point on it when I clicked the maximise button. The code then stopped at the break point proving that this function is invoked when using max / min. I guess the structure should contain info whether the user is doing a max / min ?

Thanks

David Crow13-Jul-07 4:29

David Crow

13-Jul-07 4:29

minkowski wrote:
...proving that this function is invoked when using max / min.

True, but that does not mean it is the only function involved in such a request. The WM_GETMINMAXINFO message is sent to a window when the size or position of the window is about to change. You can handle this message to override the window's default maximized size and position, or its default minimum or maximum tracking size.

The WM_SIZE message is sent to a window after its size has changed. Given your request of, "...change the way the application behaves when a user maximises the main window frame.", I'd opt for handling this message.

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

baerten12-Jul-07 23:43

baerten

12-Jul-07 23:43

I NEVER TRIED, but you can test to handle the WM_ONSIZE Message
There you get the UINT nType, which you can test on if(nType == SIZE_MEXIMIZED)

I hope it's true what i say Laugh | :laugh:

Good luck