Re: GetOpenFileName causes lock-up

From:

Giovanni Dicanio <giovanniDOTdicanio@REMOVEMEgmail.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Tue, 18 Aug 2009 10:00:30 +0200

Message-ID:

<edN52n9HKHA.1492@TK2MSFTNGP03.phx.gbl>

rik ha scritto:

Hi,
having a problem where using GetOpenFileName crashes in debug mode
only.

To test it I grabbed an example off CodeGuru and found that if I
modify the filter it will cause my program to lockup
ofn.lpstrFilter = "Text Files (*.txt)\0*.txt\0All Files (*.*)\0*.*\0";
<< this works!!
but
ofn.lpstrFilter = "Text Files (*.txt)\0*.txi\0All Files (*.*)\0*.*\0";
<< Lock-up

Could you please give us more details about "crash"?
What precise error message do you get?

The only difference I can spot between the above two filter strings is
the (wrong) extension "txi" instead of "txt" in the second filter string.

or
ofn.lpstrFilter = ""; << Lock-up
or
ofn.lpstrFilter = "\0\0"; << Lock-up

What's up?

I tried the following code on VS2008 and Vista, and it works fine in all
the three cases that you marked as "Lock-up":

<code>

//////////////////////////////////////////////////////////////////////////
// Test.cpp

#define WIN32_LEAN_AND_MEAN
#define STRICT
#include <tchar.h>
#include <windows.h>
#include <CommDlg.h>

int WINAPI WinMain(
     HINSTANCE hInstance,
     HINSTANCE hPrevInstance,
     LPSTR lpCmdLine,
     int nCmdShow
    )
{
     OPENFILENAME ofn;
     TCHAR szFileName[MAX_PATH] = _T("");
     ZeroMemory(&ofn, sizeof(ofn));

     ofn.lStructSize = sizeof(ofn);
     ofn.hwndOwner = NULL;
     ofn.lpstrFilter = _T("Text Files (*.txt)\0*.txi\0All Files
(*.*)\0*.*\0"); // case #1
// ofn.lpstrFilter = _T(""); // case #2
// ofn.lpstrFilter = _T("\0\0"); // case #3
     ofn.lpstrFile = szFileName;
     ofn.nMaxFile = MAX_PATH;
     if(GetOpenFileName(&ofn))
     {
         // Do something useful with the filename stored in szFileName

         MessageBox(NULL, szFileName, _T("Filename:"), MB_OK);
     }

     return 0;
}

//////////////////////////////////////////////////////////////////////////

</code>

// ------------ code segment ------------------
OPENFILENAME ofn;
char szFileName[MAX_PATH] = "";

I would suggest you to use a TCHAR here, and _T() decorator for "" empty
string.

ZeroMemory(&ofn, sizeof(ofn));

ofn.lStructSize = sizeof(ofn);
ofn.hwndOwner = NULL;
ofn.lpstrFilter = "Text Files (*.txt)\0*.txi\0All Files (*.*)\0*.*\0";

Again, you may want to decorate the above string with _T() to make your
code Unicode aware.

Moreover, I'm not sure if better practice would be to use a double \0 as
the terminator in the filter string, e.g. "...\0*.*\0\0".
(However, in code I tested, I put a single \0, and it seemed to work fine.)

HTH,
Giovanni