C / C++ / MFC

Nick Z.11-Apr-05 18:31

11-Apr-05 18:31

For lots of different settings, you should use serialization, xml, registry, or something else.
However, in your case, I think you probably just want to save and load a few settings and you are probably just starting the whole GUI business (thats what I understand you mean by "REAL application" Wink | ;)

). In that case I would use simple text based input/output to a text file, separating the different settings by some kind of delimeter (ie. a comma, a semi-column, or something like ;mysupercustomdelimiter). When you save to a text file settings.dat for ex., you separate all your settings by a comma. When you load you look for a comma and separate them into different settings. For actual text input/output you could use fstream's (ifstream/ofstream) I think.

This is not a very good solution in general, but it is probably enough to get you rolling.
If somebody feels this is a terrible advice, feel free to correct me and point out a better, SIMPLE way of storing settings.

Get used to getting stuck! Big Grin | :-D

It happens on daily basis when programming, at least to me. Laugh | :laugh:

Green Fuze12-Apr-05 0:35

Green Fuze

12-Apr-05 0:35

sounds like a simple idea that I can deal with Smile | :)

but how do I read from within the file (the text itself?) and write to that text?

ThatsAlok11-Apr-05 20:35

ThatsAlok

11-Apr-05 20:35

Look for [CArchive] class

[Vote One Here, Complete my Survey....]

Alok Gupta
visit me at http://www.thisisalok.tk

"I ~~Think~~ Believe this Will Help"

Green Fuze12-Apr-05 2:55

Green Fuze

12-Apr-05 2:55

I read about CFile, CArchive and CFileDialog.

I tried what I read about serializing objects (MSDN), but I keep on getting errors on the declaration.

I'm trying to change my approch to this problem and try and use a text file (what the other guy who helped me suggested).
the only thing I can't find is ow to make my app read the text from within the text file.

Thread synchronization.

Nick Z.11-Apr-05 13:50

11-Apr-05 13:50

Is it safe to have one thread periodically writing to a variable on the heap while another thread is constanly reading that variable?

I have two threads, a worker and GUI.
The worker HAS to be in a loop writing data. Now I need some way of stopping that loop from withing the GUI thread.

I thought, have a common variable "state". Constantly check that variable from withing the worker to make sure it(the worker) should still be working. Whenever I need it to stop, the GUI thread can change the "state" variable to "STOP_STATE" or something among those lines and the next time the worker checks that variable, it stops.

Something tells me this is a very wrong way of syncronizing two threads. Could someone please point me in the right direction.

Thanks in advance,
Nick Z.

Ryan Binns11-Apr-05 17:59

Ryan Binns

11-Apr-05 17:59

Your situation is a simple one, and the simple solution you propose should be fine. Just make sure that only ever one thread writes to the variable. As soon as multiple threads write to the variable, you'll have to add synchronisation (mutex, critical section etc...) to make sure that multiple writes don't happen concurrently.

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

Nick Z.11-Apr-05 18:09

11-Apr-05 18:09

For once something simple is the solution!
Thank you for clearing this up. Smile | :)

markkuk12-Apr-05 0:23

markkuk

12-Apr-05 0:23

Additionally, the shared variable must be declared volatile, so that the compiler doesn't optimize away any reads/writes of the variable.

Jack Puppy11-Apr-05 18:00

Jack Puppy

11-Apr-05 18:00

You should try using an event for this.

in the GUI thread:

<br />
// Create an event in non-signalled state that's a member variable of your dialog<br />
m_hCancelEvent = CreateEvent(NULL, TRUE, FALSE, NULL);<br />

then pass the event handle to the worker thread in the AfxBeginThread call.

The GUI can then signal the worker (say via a Stop button) using:

<br />
// Signal the event<br />
SetEvent(m_hCancelEvent);<br />

and the worker can test for that signal in the thread procedure using WaitForSingleObject (or WaitForMultipleObjects if you're tracking multiple events)

<br />
// Check for signal; Wait will return WAIT_OBJECT_0 when the event has been signalled<br />
if (::WaitForSingleObject(pYourThreadData->hCancelEvent, 0) == WAIT_OBJECT_0))<br />
  // bail out here<br />
else<br />
// do thread stuff<br />
<br />

You need to close the event when your dialog closes:

<br />
// CloseHandle will throw an exception if the handle is bad, so you should use a try block here<br />
CloseHandle(m_hCancelEvent);<br />

II)

If you need to read/write shared data between threads, it's best practice to use the appropriate sync object. This is a very simplified example.

<br />
// Global defines<br />
static CCriticalSection g_criticalSection;<br />
static int* g_pSharedValue;<br />

In Thread 1:

<br />
CSingleLock singleLock(&g_criticalSection);<br />
<br />
// Block the other thread<br />
singleLock.Lock();<br />
<br />
if (g_pSharedValue != NULL)<br />
{<br />
    // I give to you, 8 more units<br />
    *g_pSharedValue += 8;<br />
<br />
    // Then double the profits<br />
    *g_pSharedValue *= 2;<br />
}<br />
<br />
// OK, we're done, other thread can have at it now<br />
singleLock.Unlock();<br />
<br />

In Thread 2:

<br />
CSingleLock singleLock(&g_criticalSection);<br />
<br />
// Block the other thread; all statements until UnLock are atomic<br />
singleLock.Lock();<br />
<br />
// Hah! I delete your silly profits<br />
delete g_pSharedValue;<br />
g_pSharedValue = NULL;<br />
<br />
// OK, we're done, other thread can have at it now<br />
singleLock.Unlock();<br />
<br />

Without the criticial section here, Thread 2 may execute the statement "delete g_pSharedValue", and then pass control to Thread 1. g_pSharedValue is corrupt, and causes Thread 1 to barf.

Pssst. You see that little light on your monitor? That's actually a government installed spy camera. Smile and wave to big brother!

Nick Z.11-Apr-05 18:12