MFC threading question

JDoggieIII (1)
Hi,
I am using C++ MFC and I wouldn't exactly call myself an expert :-). What I have is a thread drawMonitor which monitors when to draw and I would like it to call DrawLines() (which is a member function in the class) to do the drawing.

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void drawMonitor(void *); //this is in the code file
void drawMonitor(void *arg)
{
    TCHAR buf[128];
    _stprintf(buf, _T("Draw Monitor started\n"));
    OutputDebugString(buf);
    while (true)
    {
        if (g_VangleReady)
        {
            //DrawLines();
            g_VangleReady = false;
        }
        else 
            Sleep(g_DrawMonitorDelay);
    }
    _stprintf(buf, _T("Draw Monitor stopped\n"));
    OutputDebugString(buf);
}
void CDraw2::DrawLines() 
{
    //Code here
}

I am starting my thread using _beginthread(drawMonitor, 0, (void*)12);
This builds and executes ok, but the DrawLines is commented out. When I remove the comments I get the error message: C3861: 'DrawLines': identifier not found. When I attempt to add drawMonitor to the class:

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void CDraw2::drawMonitor(void *); //this is in the header file, all else is in the code file
void CDraw2::drawMonitor(void *arg) { /* same code as above but DrawLines is not commented out */ } //in code file

I am now starting my thread using _beginthread(CDraw2::drawMonitor, 0, (void*)12);
I now get an error message C3867: 'CDraw2::drawMonitor': function call missing argument list; use '&CDraw2::drawMonitor' to create a pointer to member

I am not much a C++ progreammer, but we are trying to throw a demonstrator together which requires the use of C++ MFC. Any help with what I am doing wrong would be much appreciated as I've spent many hours trying to puzzle through this.

Thanks in advance.
Last edited on
modoran (1101)
Your CDraw2::drawMonitor method must be declared as static or use a normal function (not a member of a class).
codewalker (159)
_beginthread(drawMonitor, 0, (void*)12);
is good except you need to pass instance/object of the class CDraw2 as argument (why is the "12" even passed? its not used anyway)

like _beginthread(drawMonitor, 0, (void*)cdDrawObject);

and in the function 

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void drawMonitor(void *arg)
{
    CDraw2 cdDrawInst = (CDraw2 *) arg;
    TCHAR buf[128];
    _stprintf(buf, _T("Draw Monitor started\n"));
    OutputDebugString(buf);
    while (true)
    {
        if (g_VangleReady)
        {
            cdDrawInst->DrawLines();
            g_VangleReady = false;
        }
        else 
            Sleep(g_DrawMonitorDelay);
    }
    _stprintf(buf, _T("Draw Monitor stopped\n"));
    OutputDebugString(buf);
}


To make it work like _beginthread(CDraw2::drawMonitor, 0, (void*)12);
You need to make CDraw2::drawMonitor a static function

Now this should make it work, but if you are using MFC anyway why don't you use CWinThread/AfxBeginThread instead of _beginthread? Why mix plain windows API and MFC?

Also you need to look at synchronising threads, you are accessing global variables from the thread.

Look at http://www.codeproject.com/Articles/3539/Threads-with-MFC and http://msdn.microsoft.com/en-us/library/975t8ks0(v=vs.71).aspx
kbw (5375)
You should try to do your GUI updates from the main thread. You're asking for trouble if you have multiple threads updating the screen.
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