C / C++ / MFC

2-Jun-07 1:05

I have a program,using thirdpart code.(there are some C codes in it)
It works when I debug it step by step,but it would crash if I run it weather in release or debug mode.
I found that there are some exceptions occur.But the most strange thing is that the exception cound not be catched using CException but only be catched if I use catch(...).
Someone would tell me why?

BEST REGARDS

Rajesh R Subramanian2-Jun-07 1:11

2-Jun-07 1:11

You are probably stomping on memory that you do not own. Can you post relevant portion of the code where the crash occurs?

Nobody can give you wiser advice than yourself. - Cicero

kcynic2-Jun-07 1:27

2-Jun-07 1:27

OK,it very kind of you.
But if you give me your e-mail,that I can send the codes for you?
My E-mail is:kcynic@163.com
Thanks.

Rajesh R Subramanian2-Jun-07 1:33

2-Jun-07 1:33

kcynic wrote:
But if you give me your e-mail,that I can send the codes for you?

Please don't email me any code. Post the "relevant" code right here. By relevant, I mean the code where the crash occurs. That way, even if I can't figure out the problem, somebody else will! And the reply might be useful to someone who may search the forums for a similar problem in the future. That is the very reason behind having discussion forums.

PS: Edit your previous post to remove your email id from it. You are inviting spam by displaying your email ID on a public forum, which search engines will index.

Nobody can give you wiser advice than yourself. - Cicero

kcynic2-Jun-07 1:45

2-Jun-07 1:45

my codes is so simple,and the exception was occured in the thirdpart codes.
I don't think the error could be handled using such no sense codes.
my codes like this:

CMyODBC db;<br />
	int rows=0;<br />
	if(!db.ConnectDB("Test","sa",""))<br />
	{<br />
		AfxMessageBox("Opent the database failed!");<br />
		return;<br />
	}<br />
	CString sql="SELECT * FROM [KB_USERS_ALL]";// <br />
	CODBCSet set;<br />
<br />
	db.PrepareSql(sql,set);<br />
	try<br />
	{<br />
		db.FetchData();<br />
		CString str;<br />
		char* msg=set.m_coldata[0].value;<br />
	}<br />
	catch (...)//CException *e<br />
	{<br />
		AfxMessageBox("Exception");<br />
//		e->Delete();<br />
	}<br />
	<br />
	try{	<br />
	while(db.FetchData())<br />
	{<br />
		rows++;<br />
		CString str;<br />
		for(int i=0;i<set.GetCols();++i)<br />
			str+=set.m_coldata[i].value;<br />
		AfxMessageBox(str);<br />
	}<br />
	}catch(...)<br />
	{<br />
		AfxMessageBox("dfgdsg");<br />
	}<br />
	CString str;<br />
	str.Format("there has %d records",rows);<br />
	AfxMessageBox(str);<br />
	try{<br />
//	db.DisConnect();<br />
	}catch(...)<br />
	{<br />
		<br />
	}

But thanks all the same.
Best regards to you.

Rajesh R Subramanian2-Jun-07 2:00

2-Jun-07 2:00

You see, CException is the base class for all exceptions in MFC. I don't know an MFC class named CMyODBC. Check with your third party vendor if they have an exception handling class for their CMyODBC class.

Nobody can give you wiser advice than yourself. - Cicero

Matthew Faithfull2-Jun-07 1:59

Matthew Faithfull

2-Jun-07 1:59

Looks like your third party C may be throwing but C doesn't use CException, that's a C++ class, so catch( CException ) won't work. You could try catch( std::exception ) in case it's throwing something derived from the standard library exception. Other than that I would try catch( char* ). Believe it or not this may be the only way to trap some C exceptions short of catch(...) which really doesn't let you find out what's wrong Smile | :)

Nothing is exactly what it seems but everything with seems can be unpicked.

Rajesh R Subramanian2-Jun-07 2:02

2-Jun-07 2:02

Matthew Faithfull wrote:
Other than that I would try catch( char* ).

The Old Skool method Big Grin | :-D

Nobody can give you wiser advice than yourself. - Cicero

kcynic2-Jun-07 2:15

2-Jun-07 2:15

Yes,I know that you mean.The part C code CMyODBC only a general class using Win Database API,as you said,if there has some try block,it also doesn't throw CException.
Thanks.I would go steep into the code and find the error(because there is no try-catch block in it!)

Matthew Faithfull2-Jun-07 2:43

Matthew Faithfull

2-Jun-07 2:43

Ah Ha! You didn't say you were using ODBC. That changes everything I'm afraid. ODBC is very naughty, it uses exceptions internally to control memory allocation, so you have to be even more careful than usual. Just because ODBC is reporting an exception to the debugger when you step through the code doesn't mean there is necessarily an error. On the other hand maybe there is. D'Oh! | :doh:

It's a great example of why you should only use exceptions for handling real exceptional cases and not overload them to do other jobs Wink | ;)

The other thing to watch with ODBC is to make sure you unwind everything in the exact reverse order that you created it in the first place, even the connection dialog. Everthing you create or call to set up your connection should be undone or shutdown, as the case may be, in the exact reverse order. This isn't in the docs but if you don't do it you'll get very random crashes, sometimes only in Release builds and only with large data sets Dead | X|

. Very nasty indeed. Good luck.

Nothing is exactly what it seems but everything with seems can be unpicked.

kcynic2-Jun-07 21:40

2-Jun-07 21:40

Thanks,but I want to know why the codes didn't throw an exception when I trace it step by step,but only when I run it there would be some exception.

Matthew Faithfull3-Jun-07 2:43

Matthew Faithfull

3-Jun-07 2:43

There's no obvious reason why you'd get exceptions only when you don't run step by step but there are two related likely causes.
Stepping through the code affects two things, speed and thread synchronisation. If multiple threads are involved then the code may work when single stepped but crash when run for real if data or resouce sharing between the threads is faulty.
If it's single threaded then all you really have left is speed and unless there's any io/comms external or interprocess communication going on then the difference would be hard to explain. Usually single stepping would only make the system work if the code being run is overrunning a buffer in another, flawed, process but doesn't fill the buffer as fast when single stepped so you don't see the bug.;)
The only way you're going to get to the bottom of this is to look at what the excpetion tells you and where it occurs. Find the exception code e.g. 0xC0000005 for Access Violation and make sure the debugger is set to always break on that exception. If the debugger is being cryptic you could always post what it says and someone may recognise it. Smile | :)

Nothing is exactly what it seems but everything with seems can be unpicked.

To allign text in message box

Stephen Hewitt3-Jun-07 14:21

Stephen Hewitt

3-Jun-07 14:21

That's not scary, it's normal.

In standard C++ try/catch can only catch C++ exceptions: that is only exceptions that are raised by the C++ throw statement. Unfortunately some version of Microsoft Visual C++ (6.0 and below) do not follow the standard in this regard. This was fixed in later versions but the old non-standard behaviour can be selected with the /EHa[^] switch (not a good idea in general).

__try/__except is a low level construct and can catch any exception. Note however that with __try/__except the destructors of objects on the stack as it is unwound are not called, so this construct doesn’t play nice with C++. It will break the RAII pattern for example.

Steve

Mushtaque Nizamani2-Jun-07 0:29

Mushtaque Nizamani

2-Jun-07 0:29

Hi,

Can I allign(right,left,center) text in a message box(MessageBox or AfxMessageBox API).

Warm Regards,
Mushq

Re: To allign text in message box

Rajesh R Subramanian2-Jun-07 0:43

Inverse of a matrix(urgent:)

2-Jun-07 0:43

Mushq wrote:
Can I allign(right,left,center) text in a message box(MessageBox or AfxMessageBox API).

Left: Yes, by default.
Right: Yes, use MB_RIGHT style.
Center: Not with the standard message box. There might be custom messagebox classes around which will do it. Google for it.

Nobody can give you wiser advice than yourself. - Cicero

sujithkumarsl1-Jun-07 23:50

sujithkumarsl

1-Jun-07 23:50

i want the sample c++ code to find the inverse of a 4 by 4 matrix please help

My small attempt...

Re: Inverse of a matrix(urgent:)

Rajesh R Subramanian2-Jun-07 0:22