C / C++ / MFC

Re: Provide me all the Possible alternatives to access a member variable and member function from a global function.

27-Jul-12 21:30

You can only access the variable through the object, so you need to send a pointer to the object into the global function. Perhaps you need to look at your design.

One of these days I'm going to think of a really clever signature.

Krish6927-Jul-12 22:17

Krish69

27-Jul-12 22:17

I used a global pointer to the dialog class. I initialized the global pointer to "this" pointer inside the OnInitDialog() function. Then I used the global pointer in the global function to call the member function. The member function is called, but when I try to update values in the edit control using UpdateData(FALSE) the application crashes.

Re: Provide me all the Possible alternatives to access a member variable and member function from a global function.

Jochen Arndt27-Jul-12 22:47

Jochen Arndt

27-Jul-12 22:47

You mentioned that you are using another thread. MFC classes are not thread safe. To communicate with Windows controls from another thread, use the API PostMessage() function in your thread passing the handle of the control window. Alternatively post user defined messages and handle them in your CDialog derived class.

Re: Provide me all the Possible alternatives to access a member variable and member function from a global function.

Maximilien27-Jul-12 23:41

Maximilien

27-Jul-12 23:41

you need to send/post a message to the dialog from the thread to update the edit box.

Do not access UI element from a thread that is not the owner of the UI.

have a look at this : That's right. A worker thread must not touch a GUI object. This means that you should not query the state of a control, add something to a list box, set the state of a control, etc.[^]

Watched code never compiles.

CInvalidArg exceptions

ForNow26-Jul-12 17:36

26-Jul-12 17:36

Hi,

I am getting a CInvaliArg exception after Doing CWnd::SendMessage

The CWnd is a CDialog

The Wparam and Lparam are both pointers

The ONMESSAGE procedure has WPARAN LPARAM paramters

What Causes a CInvalid Arg Exceptions ??

Richard Andrew x6426-Jul-12 18:23

Richard Andrew x64

26-Jul-12 18:23

You could try stepping into the SendMessage function to see what causes it to bomb.

The difficult we do right away...
...the impossible takes slightly longer.

Richard MacCutchan26-Jul-12 23:00

26-Jul-12 23:00

Without seeing the exact code no one can guess what you are doing wrong.

One of these days I'm going to think of a really clever signature.

ForNow27-Jul-12 11:13

27-Jul-12 11:13

Durning The INITINSTANCE of my CWinApp I allocate via new operator a Derived CEvent class

This CLass has

1) buffer allocated via new in the contructor of a command that I use via named pipes

"WriteFIle" to get excuted in another process

2) a pointer to a CWND * type object for which I do ::SendMessage(
of the responce of that command

I use SetEvent to trgger the Write file with the contents of what is in the buffer

In My case the CWnd * is a CDialog * but that shouldn't be a problem

The corruption ??? if I allocate via new in the ::INITINSTANCE of My Main Thread
that object (derived CEvent) it should remain there for the lifetime of the prrocess

I save the pointer to that object In My main thread reterive that pointer

via AfxGetApp

Richard MacCutchan27-Jul-12 21:25

27-Jul-12 21:25

Very interesting but you need to show the exact code that causes the problem, including the code that creates any objects used in the line causing the problem. Explaining in broad terms as above does not really help.

One of these days I'm going to think of a really clever signature.

ForNow29-Jul-12 10:39

29-Jul-12 10:39

In My CWinApp:: InitInstance() I create a Derived CEventObject

mybaseeventptr = new MyBaseEvent(FALSE,FALSE,NULL,NULL); which has the following layout

C++

class MyBaseEvent : public CEvent
{
 public:
	 MyBaseEvent();   // contructer
         // CSingleLock mylock;
       MyBaseEvent(BOOL own, BOOL reset, LPCTSTR mystring, LPSECURITY_ATTRIBUTES mysec);
	    char *buffer_ptr;
         int len;
                CWnd *send_window;

};

then further down in my CWInApp::InitInstance I create a worker thread which does
WriteFile and ReadFile (named pipes IPC)

this is triggered via SetEvent from my derived MyBaseEvent Object

In Addition to triggering the event I set the CWnd * pointer of the Window were I would like the message sent to

C++

LRESULT CprogDebug::receive_tcpip(WPARAM mywparam,LPARAM mylparam)// CprogDebug message handlers
        {
		UNREFERENCED_PARAMETER(mywparam);
 
        char *hold_ptr;
        CHERC_CMDApp *main_app;
        MyBaseEvent* myeventptr;
.
.
.
.

         myeventptr->send_window = this;
       myeventptr->SetEvent();              // SHOW THE WINDOW
        return TRUE;

}

The following is the worker thread I started which has the SendMessage causing the
exception

C++

   UINT hercgui_commands(LPVOID lparam)
 {
 int i;
 CString storstrg;
 BOOL bresult;
 UNREFERENCED_PARAMETER(lparam);
 void SetThreadName( DWORD dwThreadID, LPCSTR szThreadName);
 CMutex mymutex(FALSE,"HercLock",NULL);
 CSingleLock HercLock(&mymutex);
 DWORD dwbytestoread;
 CHERC_CMDApp* main_app;
 CMainFrame *main_window;
 dwbytestoread = 1500;
 MyBaseEvent *my_event;


 main_app = (CHERC_CMDApp *)AfxGetApp();


  my_event = main_app->mybaseeventptr;

  SetThreadName(GetCurrentThreadId(),"HercGUI");

 // CSingleLock *HercLock = static_cast<Mythread *>(lparam)->HercLock;

    while(1)

         {


 WaitForSingleObject(my_event->m_hObject, INFINITE);
  if (!HercLock.IsLocked())
 {
         HercLock.Lock(INFINITE);


          WriteFile(main_app->filehdl,
                       (LPCVOID)my_event->buffer_ptr,
                        30,
                        NULL,
                        (LPOVERLAPPED) &main_app->herc_over);



  }


   bresult =    ReadFile(main_app->filehdl,
                   (LPVOID) my_event->buffer_ptr,
                    dwbytestoread,
                    NULL,
                     (LPOVERLAPPED) &main_app->herc_over1);

//  WaitForSingleObject(herc_over1.hEvent,INFINITE);
 WaitForSingleObject(main_app->herc_over1.hEvent,INFINITE);


     HercLock.Unlock();
// strncpy(&stor_buffer[0],&buffer[0],100);

        my_event->send_window->SendMessage(WM_HERCGUI_MESS,(WPARAM) my_event->len,(LPARAM) my_event->buffer_ptr);    // statement casing the exception

     i = 1;
         }
   return 0;
 }

Maybe the problem is passing pointer objects across threads ?? as maybe I should just

pass the handle of the CWnd *

Thsnks

Richard MacCutchan29-Jul-12 10:48

29-Jul-12 10:48

ForNow wrote:
Maybe the problem is passing pointer objects across threads ?

I think that is true, the SendMessage() function actually calls in to the window procedure of the main thread which is illegal. You should use the PostMessage() function which sends the message into the main thread's message queue.

One of these days I'm going to think of a really clever signature.

ForNow29-Jul-12 14:01

29-Jul-12 14:01

Using Worker Threads[^]

From the following article seems like I can only Post/SendMessage from a Worker thread

only to the MainWindow CMainFrame not to a CDialog

Chuck O'Toole30-Jul-12 2:02

Chuck O'Toole

30-Jul-12 2:02

Not true, I use PostMessage() to a CDialog based window all the time.

Note that SendMessage() cannot be used to send messages to controls that were *not* created by the thread sending the message. See my answer to This Question[^]