Solved

CFileException problem

Posted on 2001-09-13
4
1,272 Views
Last Modified: 2012-08-14
Hello all,
   I have the following code (snippet)

...
CFile szTemplateFile;
CFileException* pFileError;
CString ErrorText;

if (! szTemplateFile.Open(m_szTemplateParameterData, CFile::modeRead | CFile::shareDenyWrite, pFileError))
{
     FileErr.Clear();
     ErrorText = "Can not open file " + m_szTemplateParameterData;
     FileErr.m_lpszErrorDescription  = ErrorText;
     FileErr.m_nErrorCode = pFileError->m_cause;
...

When I pass a valid file name into the function I don't have any problems.  When I pass an invalid file name into the function I get an unhandled exception error, and I find that pFileError has no information in it.  Any ideas as to what I am doing wrong?

Thanks



0
Comment
Question by:edc
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
4 Comments
 
LVL 86

Expert Comment

by:jkr
ID: 6480885
You don't catch the exception - use

TRY {
if (! szTemplateFile.Open(m_szTemplateParameterData, CFile::modeRead | CFile::shareDenyWrite, pFileError)) {
// error
}
CATCH( CFileException* pFileError){
    FileErr.Clear();
    ErrorText = "Can not open file " + m_szTemplateParameterData;
    FileErr.m_lpszErrorDescription  = ErrorText;
    FileErr.m_nErrorCode = pFileError->m_cause;
}
0
 
LVL 1

Author Comment

by:edc
ID: 6480910
Thanks for the reply jkr.  I found that if I declare CFileException pFileException rather than CFileException* pFileException and then pass the address to the CFile::Open function that it works, although it would be nice to know why.  I will try your suggestion as well.  It never hurts to have more than one way of doing things.
0
 
LVL 86

Accepted Solution

by:
jkr earned 100 total points
ID: 6480924
Ooops, you're correct - didn't see that, as exceptions are usually handled the try/catch way. But, the MS docs also use

//example for CFile::Open
CFile f;
CFileException e;
char* pFileName = "test.dat";
if( !f.Open( pFileName, CFile::modeCreate | CFile::modeWrite, &e ) )
   {
#ifdef _DEBUG
   afxDump << "File could not be opened " << e.m_cause << "\n";
#endif
   }

0
 
LVL 49

Expert Comment

by:DanRollins
ID: 6481204
...although it would be nice to know why.

The reason is that in this line,

   CFileException* pFileError;

you declare pFileError as a pointer, but it doesn't point to anything.  If you want to use it that way, you could have used:

CFileException* pFileError= new CFileException;

Thuse, in the call to

.... Open(..., pFileError)...

you were passing an invalid pointer in to the Open call.  That caused an unhandled exception when the system tried to write some data to that address.  I'm thinkijng that the CFileException that is handled by MFC's Open fn handles regular, file-related exceptions, but not memory access exceptions.

As jkr says, the normal way to handle this is something like ...

CFileException e;
BOOL fRet=  .... Open(..., &e );
if (fRet==FALSE ) { // ERROR!!!
      char buf[256];
      e.GetErrorText( buf, sizeof(buf) );
      AfxMessageBox( buf );
}
 
-- Dan
0

Featured Post

Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
ASP.net build a IF/Then Walkthrough Guide 1 283
AVI wait icons for CAnimateCtrl in Visual Studio 2008 MFC 1 162
Which Linux flavors will this run on? 6 103
Gaming Software 1 30
In days of old, returning something by value from a function in C++ was necessarily avoided because it would, invariably, involve one or even two copies of the object being created and potentially costly calls to a copy-constructor and destructor. A…
Many modern programming languages support the concept of a property -- a class member that combines characteristics of both a data member and a method.  These are sometimes called "smart fields" because you can add logic that is applied automaticall…
The goal of the tutorial is to teach the user how to use functions in C++. The video will cover how to define functions, how to call functions and how to create functions prototypes. Microsoft Visual C++ 2010 Express will be used as a text editor an…
The goal of the video will be to teach the user the concept of local variables and scope. An example of a locally defined variable will be given as well as an explanation of what scope is in C++. The local variable and concept of scope will be relat…

730 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question