The advice here and your website have been very helpful. My practice
understanding is much clearer.
Joseph M. Newcomer wrote:
See below...
On Wed, 12 Mar 2008 20:41:14 -0400, Jeffro <jeffadamczak@hotmail.com> wrote:
I'm trying to learn threads so I started a C++ MFC app in Visual Studio
2008. It's a single dialog based app with an Edit control, a Run button
and an Exit button. The Run button sends updates to the edit control in
a continual loop. How do I get the program to respond to events? That
is, to close when I press the Exit button? Do I even need a thread in
this situation? Even if threads aren't necessary, please show me how it
would be done (with threads).
****
The code below is completely wrong, and exhibits the problem of NOT using threads. You
have blokced the GUI forever; it will not respond to keyboard input, mouse input, menus
are dead, every control is dead, dead, dead. This is a classic example of
worst-possible-design.
See my essay on worker threads on my MVP Tips site. The rules don't change whether it is
an SDI, MDI, or dialog-based app.
Using antiquated and dangerous functions like _itoa, obsolete data types like 'char', and
fixed-size buffers represent some of the worst possible practices available today.
It is unclear why you are using 'char' and calling 'SetWindowTextW'; this makes no sense
at all.
It is generally safe to make the following assumptions
Fixed arrays of char are a design error
Use of _itoa or similar functions is a design error
Use of 8-bit characters is a design error
Calling a W-suffixed method is a design error
Lengthy loops in the main GUI thread are a design error
Use of exit() is ALWAYS, WITHOUT EXCEPTION a design error
Once you understand the basic ideas, you will see that there are times when these are the
only possible design options in certain rare and exotic cases, none of which exist here.
Except for the exit() case, which is ALWAYS wrong.
The correct code is very simple
void CThreadPracticeDlg::OnBnClickedRun()
{
running = TRUE;
AfxBeginThread(threadfunc, this);
}
/*static */ UINT CThreadPracticeDlg::threadfunc(LPVOID p)
{
CThreadPracticeDlg * me = (CThreadPracticeDlg*)p;
me->RunThread();
return 0;
}
void CThreadPracticeDlg::RunThread()
{
int i = 0;
while(running)
{ /* thread loop */
i = (i + 1) % 10;
CString * t = new CString;
t->Format(_T("%d"), i);
PostMessage(UWM_DATA, (WPARAM)t);
Sleep(500);
} /* thread loop */
use a user-defined message for UWM_DATA; see my essay on message management.
#define UWM_DATA (WM_APP + 100)
ON_MESSAGE(UWM_DATA, OnData)
LRESULT CThreadPracticeDlg::OnData(WPARAM wParam, LPARAM)
{
CString * t = (CString *)wParam;
m_edit1.SetWindowText(*t);
delete t;
return 0;
}
void CThreadPracticeDlg::OnStop()
{
running = FALSE;
}
This is the simplest code. Nothing has been done here to stop you from clilcking the run
button and getting many concurrent threads, but that is a decision you have to make as to
whether or not you want to allow that. If you do so, you need to have the thread do a
PostMessage telling you it is completed before the thread function exits, and when you
receive that message you re-enable the button. See my essay on dialog control management.
Strictly speaking, in this trivial case of a single integer you could have simply done a
PostMessage of the integer, but that is so rarely the case in real programs that I have
shown the more general solution here.
****
void CThreadPracticeDlg::OnBnClickedRun()
{
int i = 0;
while (1) {
if (i >= 10) {
i = 0;
}
char intString[2];
_itoa(i,intString,10);
CString msg = CString(intString);
m_edit1.SetWindowTextW(msg);
i++;
Sleep(500);
}
}
void CThreadPracticeDlg::OnBnClickedExit()
{
exit(0);
****
COMPLETELY WRONG! NEVER, EVER CALL THIS FUNCTION, OR ANY EQUIVALENT FUNCTION, IN A
WINDOWS APP!!!!!!
joe
****
}
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Joseph M. Newcomer [MVP]
email: newcomer@flounder.com
Web: http://www.flounder.com
MVP Tips: http://www.flounder.com/mvp_tips.htm
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