how to break out infinite loop?

I want to know in the infinite loop, how to keep track if user hit any key especially ESC key then break out of infinite loop.

Here is my code:

for (;;)
{
// please help me to figure it out this section here how to keep track if user hit any key
// waiting user to hit any key
// if user hit ESC key then break;
// otherwise
.... my tasks.....
..................
}

1. Set a member variable to false before entering your loop.
2. When you enter the loop, set a flag variable to show you're in the loop, and upon exiting the loop, reset the flag variable.
3. Use ClassWizard to set up a PreTranslateMessage() handler.
3. In the PreTranslateMessage(0 handler, look for key down. If the key is escape, and you're in your loop, set the member variable mentioned in step 1 to true.


Sample code:


// in your class header file
bool m_bBreak; // will be true when loop needs to stop
bool m_bInLoop; // only true when inside our loop

// PreTranslateMessage() handler in your implementation file:
BOOL CMyClass::PreTranslateMessage(MSG* pMsg)
{
if (pMsg->message == WM_KEYDOWN && pMsg->wParam == VK_ESCAPE && m_bInLoop)
m_bBreak = true;

return CDialog::PreTranslateMessage(pMsg);
}

// your loop:
m_bBreak = false;
m_bInLoop = true;
while(!m_bBreak)
{
// Do your loop processing here.
// When user hits the escape key, the handler will set m_bBreak to true,
// causing your loop to exit
}
m_bInLoop = false;

Well you have written it already...


for(;;){
if( need to break )
break;
}




the break; will break out of the loop you are in, if you are in nested loops, it will break out of the inner and continue in the outer loop. A not very nice one but effective with many nested loops is to set a label and use goto.



Regards Albert Bertilsson
http://www.albert.nu

Hi Bob,
I try it your way, but still not working. When Spy_Terminal function trigger, I try to hit ESC key doesn't do anything. Look like the while loop still running.

Please show me where am I making mistake. Thanx in advance for helping me.

void CAdSetupView::Spy_Terminal()
{
unsigned short port_error;
CString strComMsg;
CString strSpyMsg;

MyComLink sio ( ComPortDlg.iComPort );
GFSerial cp ( &sio );

// Check for invalid com port
if (cp.GetCommError(port_error) != GCPP_OK)
{
strComMsg.Format ("%d", ComPortDlg.iComPort+1);
MessageBox ("Com " + strComMsg + " is not valid. Please pick a different Com Port.", "Invalid Com Port", MB_OK | MB_ICONSTOP);

if (IDOK)
return;
}
else
{
// flush characters from the receive buffer so we get new msg
cp.RXFlush();
bBreak = false;
bInLoop = true;
while (!bBreak)
{
cp.GetString (rcv_Spy, 500, '0x03', 500);
m_strSpyMode.Format ("%s", rcv_Spy);
UpdateWindow();
UpdateData(false);
}
bInLoop = false;
m_strSpyMode = "Congratulation! You got it.";
UpdateData(false);
}
}

BOOL CAdSetupView::PreTranslateMessage(MSG* pMsg)
{
// TODO: Add your specialized code here and/or call the base class
if (pMsg->message == WM_KEYDOWN && pMsg->wParam == VK_ESCAPE && bInLoop)
bBreak = true;

return CFormView::PreTranslateMessage(pMsg);
}

Where is bBreak declared?

Set a breakpoint in PreTranslateMessage() at the "if(p->Msg == WM_KEYDOWN.." line (not on the "bBreak = true;" line), then run your program and hit the ESC key. Does the breakpoint get hit?

bBreak declared in CAdSetupView class as public.
I did set the break point on if (p->Msg....)
it did hit it when the infinite function not trigger. Once the infinite loop trigger it never hit the break point.

I think I've answered this type of question half-a-dozen times. Here's a link to one of them:

http://www.codeguru.com/bbs/wt/showp...age=0&Limit=25

Regards,
Alvaro

If the while loop processing is done as a result of some input message, like a mouse click or key stroke then the call to PreTranslateMessage likely won't happen until the looping returns. I think you need to look closer at multi threading this.

HTH.

In this case, I just want infinite loop running until the user hit ESC key then break out of infinite loop. Do you have any idea how to do this? Please let me know. Thanx in advance and I really appreciated for all the ideas and opinions.

An easy way to do this is


for (;;)
{
//do your stuff
if (GetAsyncKeyState(VK_ESCAPE)<0) break;
}




So you don't have to use the pretranslates/messagepumps/threads

Hope this helps,

Steven

#include <conio.h>

for(...)
{
if(kbhit())
{
DestroyWindow();
}
}

or just put it into the OnKeyDown function

for(...)
{
if(nChar == VK_ESCAPE)
{
DestroyWindow();
}
}

I want to detect if user hit pause key then pause the screen. I don't know what value gonna return if I check VK_PAUSE. Thanx Steve.

ESC key return less than 0.
Pause key return What value?????????????
character return What value?????????????