C / C++ / MFC

Can someone explain this please

27-Jan-05 10:49

Does LogonUserEx() help?

"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow

Tom Wright27-Jan-05 5:22

27-Jan-05 5:22

If I create a function in an MFC app that does not reference the class, how can I get it to see any pointers that I have in this function

any point that is placed in this function works:

 <br />
void CMyThread::OnClose()<br />
{<br />
<br />
}<br />

any point or variable referecnes in this function will not work

<br />
void OnClose()<br />
{<br />
<br />
}<br />

I know it won't because I'm not referencing my class any more. So how can I get it to work with out referencing my class?

God i hope this make sense

Thanks

Tom Wright
tawright915@yahoo.com

David Crow27-Jan-05 5:25

27-Jan-05 5:25

If you want the OnClose() function that is not a member of CMyThread to be able to access CMyThread's member variables, those variables would need to be static.

"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow

Tom Wright27-Jan-05 5:34

27-Jan-05 5:34

I have another program that has this code snippet in it:

<br />
__declspec(dllexport)int LA_OnSend(char* EmailAddress, char* EmailMessage) <br />
{<br />
	AFX_MANAGE_STATE(AfxGetStaticModuleState());<br />
<br />
	CLASendMailApp* sendmail = (CLASendMailApp* )AfxGetApp();<br />
	if (!sendmail->LoadSettings())<br />
	{<br />

Can you tell me what this is doing here?
CLASendMailApp* sendmail = (CLASendMailApp* )AfxGetApp();

Thanks

Tom Wright
tawright915@yahoo.com

C^hris L^osinger27-Jan-05 5:38

27-Jan-05 5:38

AfxGetApp returns a pointer to a CWinApp object.

(CLASendMailApp* )AfxGetApp() casts that pointer to a pointer to a CLASendMailApp. that way, any functions called through that pointer will act on your CLASendMailApp application, and not on the CWinApp base class.

why ? CWinApp doesn't have a LoadSettings() member function. CLASendMailApp (hopefully) does.

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Tom Wright27-Jan-05 5:44

27-Jan-05 5:44

Okay so if I need to access a function that is in another class that I have I can "cast" it like this? Can I cast down to a certain function in my class?

And in my first example can I cast a pointer to me class in the

void OnClose function?

Thanks

Tom Wright
tawright915@yahoo.com

C^hris L^osinger27-Jan-05 5:51

27-Jan-05 5:51

Tom Wright wrote:
I need to access a function that is in another class that I have I can "cast" it like this?

you can only safely cast a pointer like this if the To and From class are realted to each other (ie. if the To class is derived from the From class, or vice versa).

Tom Wright wrote:
And in my first example can I cast a pointer to me class in the void OnClose function?

you can't cast a class pointer to something that isn't a class. if you need pointers to your class in a function that isn't a member of your class, you'll need to pass a pointer to an object of your class into that function (or maybe make it available as a global variable):

void CMyClass::someFunc()
{
 NonMemberFunc(this);
}

void NonMemberFunc(CMyClass *pMyClassPtr)
{
   pMyClassPtr->someFunc();
}

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Tom Wright27-Jan-05 10:48

27-Jan-05 10:48

So Chris is it possible to redefine a function such as:

<br />
static void CALLBACK TimerProc(HWND hwnd, UINT uMsg, UINT_PTR idEvent, DWORD dwTime)<br />

To include CMyClass *pMyClassPtr, so that I would have access to all the objects in CMyClass?

<br />
static void CALLBACK TimerProc(HWND hwnd, UINT uMsg, UINT_PTR idEvent, DWORD dwTime)<br />
{<br />
	if (idEvent == 1)<br />
	{<br />
		KillTimer (NULL,idEvent);<br />
		CString mySelect;<br />
		mySelect.Format("UPDATE EMG3 SET EMG3_STATUS_DATE = CURRENT_TIMESTAMP WHERE EMG3_DEST_ID = '%s'", thdID);<br />
		m_pConnection->Execute(_bstr_t(mySelect),NULL, NULL);<br />
		SetTimer(NULL,1,m_nHearbeat*1000,NULL);<br />
	}<br />

That way i can access thdID and m_pConnection. Is this right?

Thanks

Tom Wright
tawright915@yahoo.com

C^hris L^osinger27-Jan-05 10:55

27-Jan-05 10:55

Tom Wright wrote:
To include CMyClass *pMyClassPtr, so that I would have access to all the objects in CMyClass?

i think you'd have to make those variables global, for that function to be able to use them.

maybe if you could expand on what you're trying to accomplish, i could give better answers. just pointing out C/C++ syntax errors probably doesn't help you much.

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Tom Wright27-Jan-05 11:09

27-Jan-05 11:09

I'm trying to setup a Timer in my UI thread. While doing this I found that the easiest way was to do the SetTimer with the forth parameter being the callback function.

Problem is that I've never really worked with callback function and while working with this particular one I found that i did not have access to m_pconnection pointer and the thdID pointer.

I remembered that someone had helped me with another program that did a casting of a pointer like the one listed at the beginning of the post, but i wasn't sure if this is what I needed to do here and since i didn't really understand what was happening with that line of code I decided to post.

So comming full circle I'm still trying to understand when one needs to cast a pointer and when one needs to pass a pointer.

Heck I just found out how to initialize a char array on the fly (so to speak) using the new operator. I've always seen it used but never understood why until it was explained to me.

Thanks

Tom Wright
tawright915@yahoo.com

C^hris L^osinger27-Jan-05 12:07

27-Jan-05 12:07

Tom Wright wrote:
I'm trying to setup a Timer in my UI thread. While doing this I found that the easiest way was to do the SetTimer with the forth parameter being the callback function.

if you're doing this in an MFC app, you can just use the OnTimer function to handle this: use the class wizard, if you're using VC6, or change the window/dialog/app properties in VC7, to add a handler for WM_TIMER. that way, the function will be a member of your CWnd and you can use any class functions you want.

the problem with the callback method, in my opinion, is that it doesn't give you a way to pass any custom info into the callback function. some callbacks give you a parameter that you can use for things like pointers. this one requires you to get all the data from global variables.

Tom Wright wrote:
So comming full circle I'm still trying to understand when one needs to cast a pointer and when one needs to pass a pointer.

you pass a pointer when you need a pointer to something.

you cast a pointer when the pointer doesn't point to what you need it to point to, but can safely interpreted as if it was pointing to what you need. for example, if you have a pointer to an object of type C, you can cast that pointer to anything that C is derived from; this lets you call functions from the base classes; ex. if class C is derived from class B, you can cast your C* pointer to B* and then call class B's functions. likewise, if you have a C* pointer (a pointer to an object of type C), and you've cast it to a base class of type "B" ( B* pB = (B*)pC; ), you can cast that back up to a "C". but, all this requires that you know what the pointer is really pointing to, and what the class heirarchy looks like.

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David Crow27-Jan-05 5:42

27-Jan-05 5:42

It is casting the return value of AfxGetApp() from a CWinApp* to a CLASendMailApp* so that the LoadSettings() method can be accessed.

In the past, I've always added this to my app's .h file right below the class declaration so that I did not have so many of those casts staring at me:

#define GetSendMailApp() (((CLASendMailApp*)AfxGetApp()))

Then to use it:

CLASendMailApp* sendmail = GetSendMailApp();

"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow

Tom Wright27-Jan-05 5:49

27-Jan-05 5:49

David if I were to look this up in the MSDN would it be pointer casting or just casting?

Thanks

Tom Wright
tawright915@yahoo.com

David Crow27-Jan-05 5:53

27-Jan-05 5:53

Tom Wright wrote:
if I were to look this up in the MSDN...

Like this?

"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow

Tom Wright27-Jan-05 10:26