C / C++ / MFC

Stuart Dootson1-Jul-09 3:34

1-Jul-09 3:34

I'd suggest rewriting it so that you don't need to close it to write items to the file - you've identified opening the file as the hotspot, so remove the sdcenario that means you have to open it so often. The std::basic_ostream::flush()[^] method could prove useful, to ensure the message is actually pushed to disk.

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Cedric Moonen1-Jul-09 3:35

Cedric Moonen

1-Jul-09 3:35

Souldrift wrote:
The time stealer seems to be the opening and closing of the file for every log entry. But I cannot simply open it once and never close it, because the log entrys are only put into the file with the close() call.

Even when you flush the data to the file (calling the flush method) ?

Cédric Moonen
Software developer

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Michael Schubert1-Jul-09 4:01

Michael Schubert

1-Jul-09 4:01

Create a buffer in memory, for example a string array, collect your data in this array for a certain amount of time (or a certain number of entries) and then write the contents to the file in one go.

David Crow1-Jul-09 4:52

David Crow

1-Jul-09 4:52

File I/O, especially opening, is very expensive. You may want to implement it in a separate thread so that the primary thread can run unimpeded.

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Joe Woodbury1-Jul-09 6:06

Joe Woodbury

1-Jul-09 6:06

Get rid of buffered I/O calls.

Use either purely native calls (CreateFile()) or at least the CRT open function.

If that's still too slow, using asynchronous writes (yes, they are tricky, but they do work.) Do understand that you may need a mechanism to throw away messages else you're logging could get permanently behind.

An alternative is to write log string to a buffer and when it passes 4k, do an asynchronous write.

Chuck O'Toole1-Jul-09 10:31

Chuck O'Toole

1-Jul-09 10:31

The bad news is that if you are using a Logger Class to dump output somewhere in case your program crashes, then Open / Append / Close is the only way to make sure that critical "trace" messages are not left in memory at the crash. All the other suggestions, buffering, asynch I/O, can improve the speed at the expense of the exact reason to have a logger for debug tracing.

Bite the bullet and live with the slower code. Here's what I use which includes a timestamp in the output, modify it as you see fit. Also, since this is in a class derived from a synchornized object (which has a Lock/Unlock function), this is threadsafe.

// Add a line of text to the Log
void Logger::LogThis(CString Text)
{
    SYSTEMTIME cur_time;
	CString t1;
	CString t2;
	DWORD dwBytesWritten;

	if (Folder.IsEmpty() || Prefix.IsEmpty())
	{
		TRACE("Log Location Not Set");
		return;
	}
	Lock();													// force single file to the log file
    GetLocalTime(&cur_time);
	t1.Format("%02d-%02d-%04d %02d:%02d:%02d : %.200s\r\n",
		      cur_time.wMonth, cur_time.wDay, cur_time.wYear,
		      cur_time.wHour, cur_time.wMinute, cur_time.wSecond, Text);
	t2.Format("%s%s%04d%02d%02d.log", Folder, Prefix, cur_time.wYear, cur_time.wMonth, cur_time.wDay);
	HANDLE hAppend = CreateFile(t2,	// open log file
			FILE_APPEND_DATA,		// open for writing
			FILE_SHARE_READ,		// allow multiple readers
			NULL,				// no security
			OPEN_ALWAYS,			// open or create
			FILE_ATTRIBUTE_NORMAL,	// normal file
			NULL);				// no attr. template
	if (hAppend != INVALID_HANDLE_VALUE)
	{
		SetFilePointer(hAppend, 0, NULL, FILE_END);
		WriteFile(hAppend, (LPCTSTR)t1, t1.GetLength(), &dwBytesWritten, NULL);
		CloseHandle(hAppend);
	}
	Unlock();												// OK, file is ready for the next guy
}

And it's created with:

TheLogFile = new Logger();
TheLogFile->SetFolder("Log\\");
TheLogFile->SetPrefix("UpdateProcess");

Souldrift1-Jul-09 21:54

Souldrift

1-Jul-09 21:54

Thanks for all the answers (and the code).
I came up with the buffering idea, as well - and I´m using it now. I only buffer 10 messages, then write. Seems to be enough to get rid of my real-time problems. Problem is I cannot simply 'bite the bullet', since the project is about audio streaming. And the stream is very corrupted when the logger opens a file every time. I also already built a locking mechanism.

Now I´ll see about flushing the stream. If it doesn´t work I´ll have to live with the small buffer ... for now.

Btw, are CreateFile() and WriteFile() significantly different from what I do? Ofstream open() and '<<' ?

Thanks

Souldrift

how to detect Listctrl check box selection/deselection

Michael Schubert1-Jul-09 23:25

Michael Schubert

1-Jul-09 23:25

Souldrift wrote:
Btw, are CreateFile() and WriteFile() significantly different from what I do? Ofstream open() and '<<' ?

Using CreateFile() gives you all the control (Performance/Sharing/Security) the Win32 API has to offer.

hemlat1-Jul-09 1:22

Re: how to detect Listctrl check box selection/deselection

1-Jul-09 1:22

Hi,

In my application I have created Listctrl on dialog with check box option.I need to handle check box selection or deselection events.Can anyone tell me which message handle I need to take.

Regards,
Rekha.

Jijo.Raj1-Jul-09 1:45

Jijo.Raj

1-Jul-09 1:45

Hello Hamlat,

You can use CListCtrl::GetCheck()[^]. Please have a look at this article[^].

Regards,
Jijo.

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Re: how to detect Listctrl check box selection/deselection

hemlat1-Jul-09 2:04

Re: how to detect Listctrl check box selection/deselection

1-Jul-09 2:04

Thanks for your replay. But I need to get check box event selection message handler not whether check box is checked or not.

Stuart Dootson1-Jul-09 2:40

Re: how to detect Listctrl check box selection/deselection

1-Jul-09 2:40

hemlat wrote:
Thanks for your replay. But I need to get check box event selection message handler not whether check box is checked or not.

Doesn't matter whether you need it or not - Microsoft don't provide that.

What you do have is LVN_ITEMCHANGING[^] and LVN_ITEMCHANGED[^], which are sent when an item changes in any way - it's up to you to determine if that's because a check box has changed from checked to unchecked or unchecked to checked.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

hemlat1-Jul-09 3:08

Re: how to detect Listctrl check box selection/deselection

1-Jul-09 3:08

Hi,

I have used both LVN_ITEMCHANGING and LVN_ITEMCHANGED . But these these are sent not only for check box selection but also for another events like adding items to Listctrl.

I have searched for this requirement but I did not get required result. I am not sure whether Microsoft provide this or not. I am new to MFC.

Thanks for your reply. I think I need to change logic of my code dependence on existing event handlers.

CPallini1-Jul-09 3:21

CPallini

1-Jul-09 3:21

hemlat wrote:
I have used both LVN_ITEMCHANGING and LVN_ITEMCHANGED . But these these are sent not only for check box selection but also for another events like adding items to Listctrl.

From MSDN [^]

Parameters

    pnmv

        Pointer to an NMLISTVIEW structure that identifies the item and specifies which of its attributes are changing.

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Re: how to detect Listctrl check box selection/deselection

hemlat1-Jul-09 20:46

Re: how to detect Listctrl check box selection/deselection

1-Jul-09 20:46

Thanks for your reply.I got it.

Stuart Dootson1-Jul-09 3:31

Re: how to detect Listctrl check box selection/deselection

1-Jul-09 3:31

hemlat wrote:
I have used both LVN_ITEMCHANGING and LVN_ITEMCHANGED . But these these are sent not only for check box selection but also for another events like adding items to Listctrl.

That's right. So you (YOU) need to add code to those handlers to determine whether or not an items check state has changed. Here's a hint - the checkbox is implemented as an state image overlay - look up LVIS_STATEIMAGEMASK in the list-view item state flags.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

hemlat1-Jul-09 20:47

1-Jul-09 20:47

Thanks for your reply. I got it.

abstract class

MozhdehQeraati1-Jul-09 0:31

MozhdehQeraati

1-Jul-09 0:31

Hi I am a new comer in C++. I have an MFC application that using some header files and libraries. I set the 'additional library directories' and 'additional include directories' in project settings. But whenever I want to make an instance of one of those classes I get this error:

error C2259: cannot instantiate abstract class due to the following members: ....

It is wierd as it works in another project same as this one, and there are some other classes in the lib files as this class, but the error doesn't occur in those conditions.

I know the concept of abstract class. Please help me in advanse.
Thanks

Re: abstract class

Stuart Dootson1-Jul-09 0:46