Problem with CFileDialog (access violation).

[BungoMan]

I'm having some nasty problems with the MFC class CFileDialog. I'm simply trying to use it to get the name of a selected file and put it in a text edit box. I have done this many times before and have never had this sort of problem. Here is the code that is producing the error:

void CFileSplitterDlg::OnButtonOpenSplitFile() 
{
     CFileDialog FileOpen(TRUE,0,0,OFN_HIDEREADONLY|OFN_OVERWRITEPROMPT,0,this);

     FileOpen.m_ofn.lpstrTitle="Select File to Split";

     int Result=FileOpen.DoModal();

     if (Result==IDOK)
     {
          SetDlgItemText(IDC_EDIT_SPLIT,FileOpen.GetPathName());
          m_ProgressSplit.SetPos(0);
     }
     else
     {
          if (Result==IDCANCEL)
          {
               SetDlgItemText(IDC_EDIT_SPLIT,"");
          }
     }
}

IDC_EDIT_SPLIT is defined, and m_ProgressSplit is a valid member variable. I also looked up on the MSDN anything I could find on CFileDialog and access violations and found something regarding custom CFileDialog classes and access violations, the issue is apparently fixed in windows 2000 (I'm running XP Pro), and is also fixed in VS6SP6 (I was running VS6 with no service pack when I encountered this error, I have since upgraded to SP6, this of course did not help), so I'm pretty sure it's not that I'm missing anything. Originally I was using MFC dlls, I tried switching to static MFC libraries to see if that had any effect, it didn't. I also tried created a brand new dialog based MFC application and made it so the only thing it did was create a CFileDialog when the default 'OK' button was pressed. I got the same error (which leads me to believe it is not something isolated to my project).

I've narrowed it down to the destructor of CFileDialog. When I press the 'Open Split File' (which calls CFileSplitterDlg::OnButtonOpenSplitFile()) button the CFileDialog is created and DoModal() is called (causing the dialog to appear). It then lets me select a file. If I press 'Open' it returns IDOK and the file name gets put into the text edit box. If I select 'Cancel' IDCANCEL is returned and anything inside the text edit box is cleared (as it should be). The error doesn't occur untill the destructor is called. Which of course happens when the CFileDialog goes out of scope as soon as the function. Everything I have before then works correctly (I used message boxes to stop determine the point just before it crashes). I even commented out everything but the constructor and still got an error when the destructor is called.

The error message it says when the program crashes when I run it through the debugger says, "Unhandled exception in File Splitter.exe (KERNEL32.DLL): 0xC0000005: Access Violation."

Here is the call stack the debugger gives me.

KERNEL32! 77e778ce()
CFileDialog::~CFileDialog() + 71 bytes
CFileSplitterDlg::OnButtonOpenSplitFile() line 198 + 18 bytes
_AfxDispatchCmdMsg(CCmdTarget * 0x0012fd74 {CFileSplitterDlg}, unsigned int 1007, int 0, void (void)* 0x00401078 CFileSplitterDlg::OnButtonOpenSplitFile(void), void * 0x00000000, unsigned int 12, AFX_CMDHANDLERINFO * 0x00000000) line 88
CCmdTarget::OnCmdMsg(unsigned int 1007, int 0, void * 0x00000000, AFX_CMDHANDLERINFO * 0x00000000) line 302 + 39 bytes
CDialog::OnCmdMsg(unsigned int 1007, int 0, void * 0x00000000, AFX_CMDHANDLERINFO * 0x00000000) line 97 + 24 bytes
CWnd::OnCommand(unsigned int 1007, long 2818546) line 2099
CWnd::OnWndMsg(unsigned int 273, unsigned int 1007, long 2818546, long * 0x0012f82c) line 1608 + 28 bytes
CWnd::WindowProc(unsigned int 273, unsigned int 1007, long 2818546) line 1596 + 30 bytes
AfxCallWndProc(CWnd * 0x0012fd74 {CFileSplitterDlg hWnd=???}, HWND__ * 0x00a3027a, unsigned int 273, unsigned int 1007, long 2818546) line 215 + 26 bytes
AfxWndProc(HWND__ * 0x00a3027a, unsigned int 273, unsigned int 1007, long 2818546) line 379
USER32! 77d67b17()
USER32! 77d6cdce()
USER32! 77d45696()
USER32! 77d461f6()
USER32! 77d5ec02()
USER32! 77d5c3f6()
USER32! 77d67b17()
USER32! 77d6cdce()
USER32! 77d44435()
USER32! 77d49611()
USER32! 77d5d704()
CWnd::IsDialogMessageA(tagMSG * 0x005f58dc {msg=0x00000202 wp=0x00000000 lp=0x00060017}) line 182
CWnd::PreTranslateInput(tagMSG * 0x005f58dc {msg=0x00000202 wp=0x00000000 lp=0x00060017}) line 3435
CDialog::PreTranslateMessage(tagMSG * 0x005f58dc {msg=0x00000202 wp=0x00000000 lp=0x00060017}) line 92
CWnd::WalkPreTranslateTree(HWND__ * 0x00a3027a, tagMSG * 0x005f58dc {msg=0x00000202 wp=0x00000000 lp=0x00060017}) line 2678 + 18 bytes
CWinThread::PreTranslateMessage(tagMSG * 0x005f58dc {msg=0x00000202 wp=0x00000000 lp=0x00060017}) line 672 + 18 bytes
CWinThread::PumpMessage() line 848 + 30 bytes
CWnd::RunModalLoop(unsigned long 4) line 3489 + 19 bytes
CDialog::DoModal() line 539 + 12 bytes
CFileSplitterApp::InitInstance() line 52 + 11 bytes
AfxWinMain(HINSTANCE__ * 0x00400000, HINSTANCE__ * 0x00000000, char * 0x00141f3c, int 1) line 39 + 11 bytes
WinMain(HINSTANCE__ * 0x00400000, HINSTANCE__ * 0x00000000, char * 0x00141f3c, int 1) line 30
WinMainCRTStartup() line 198 + 54 bytes
KERNEL32! 77e7eb69()

And here is a disassembly immediately surrounding the code that execution stops on.

77E778BE   xor         eax,eax
77E778C0   jmp         77E77554
77E778C5   mov         ecx,dword ptr [esp+4]
77E778C9   mov         eax,0FFFFFFFFh
77E778CE   lock xadd   dword ptr [ecx],eax
77E778D2   dec         eax
77E778D3   ret         4

It apparently stops on 77E778CE. It would appear that the pointer in ecx is a bad pointer (NULL or outside the program's memory space). I'm not 100% sure what lock xadd does, I googlged for it and it appears to have to do with threads and making it so another thread can't mess upo a counter of somekind. I'm wondering why it doesnt crash on 77E778C5... or is all that happens there is the value pointed to on the stack pointer+4 being put into ecx and that is used as a pointer? I'm not good with pointers in assembly (I don't know the syntax well enough) so I don't know if I really know what I'm talking about.

Either way it seems like it ends up with an invalid pointer. My biggest question is why? I have not done anything out of the ordinary. I followed all the examples I've found that use CFileDialog (even the one on MSDN) exactly as they were presently (sans a few minor changes that shouldn't cause an error like this). I don't understand why it used to work and now it doesn't (in any new or old project).

Any help on this would be grealty appreciated. I'm at a total loss here. This far exceeds my ability...

 

[PerFnurt]

There is nothing apparent fishy about your code. Have you tried an undconditional RebuildAll?

/Per
[sub]
"It was a work of art, flawless, sublime. A triumph equaled only by its monumental failure."[/sub]

 

[Salem]

When problems are in constructors and destructors, and everthing seems OK (even to the point of working perfectly in other parts of the program or in isolation), then its likely to be a memory access problem somewhere else in the program.

Examples of which are
- use before allocation
- use after deallocation
- use of uninitialised pointers
- stepping off the ends of allocated arrays

However, where you make the mistake (the cause) and where you notice (the effect - like your dialog) are often far removed from one another (both in time and areas of the code involved).

Use this to see if you can enable various debug options to detect where the cause of the problem is.

--

 

[ferrari123]

Hi ,
There seems to be something wrong with the way CFileDialog is definaed itself. try on different machine or reinstall visual studio.If it works then there is wrong with the defination.

thanks & regards,
~ Rudresh