Trouble using Win32 OpenFile dialog box in OpenCV

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Win32

dialog

Unicode

Dear Colleagues,

I'm attempting to use a dialog box to select the filename of an AVI file that I want to use in OpenCV. The OpenCV function is called: cvCaptureFromAVI. To create the Open File dialog box, I am using the Windows function:
GetOpenFileName

I suspect that the trouble I am having has something to do with the fact that my whole project is written in Unicode, and the OpenCV function expects const char*. If I hard-code the AVI filename as a char* variable, and I don't open the dialog box, everything seems to work. However, as soon as I try to use the dialog box, the cvCaptureFromAVI function won't work. In other words, even if I don't use the filename stored from the dialog box, I still won't be able to use my AVI file. Just opening the dialog box itself seems to screw it up.

Here is what works:

char filename[40] = "C:\\Users\\weylspinor\\Desktop\\test.avi";
CvCapture *G_movie_file = cvCaptureFromAVI(filename);

Now if I add the following, it doesnt work. (Note, I'm not even using the filename stored in the OPENFILENAME structure):

OPENFILENAME ofn;       // common dialog box structure
char szFile[260] = "";       // buffer for file name
HANDLE hf;              // file handle

// Initialize OPENFILENAME
ZeroMemory(&ofn, sizeof(ofn));
ofn.lStructSize = sizeof(ofn);
ofn.hwndOwner   = h_main;
ofn.lpstrFile   = LPWSTR(szFile);

// Set lpstrFile[0] to '\0' so that GetOpenFileName does not
// use the contents of szFile to initialize itself.
ofn.lpstrFile       = LPWSTR(szFile);
ofn.nMaxFile        = sizeof(szFile);
ofn.lpstrFilter     = TEXT("Text Files (*.txt)\0*.txt\0All Files (*.*)\0*.*\0");
ofn.nFilterIndex    = 1;
ofn.lpstrFileTitle  = NULL;
ofn.nMaxFileTitle   = 0;
ofn.lpstrInitialDir = NULL;
ofn.Flags           = OFN_PATHMUSTEXIST | OFN_FILEMUSTEXIST;


// Display the Open dialog box.
if (GetOpenFileName(&ofn) == TRUE) {
    hf = CreateFile(ofn.lpstrFile,
        GENERIC_READ,
        0,
        (LPSECURITY_ATTRIBUTES) NULL,
        OPEN_EXISTING,
        FILE_ATTRIBUTE_NORMAL,
        (HANDLE) NULL);
}

char filename[40] = "C:\\Users\\weylspinor\\Desktop\\test.avi";
CvCapture *G_movie_file = cvCaptureFromAVI(filename);

I can get it to work again by just commenting out the GetOpenFileName function.

OPENFILENAME ofn;       // common dialog box structure
char szFile[260] = "";       // buffer for file name
HANDLE hf;              // file handle

// Initialize OPENFILENAME
ZeroMemory(&ofn, sizeof(ofn));
ofn.lStructSize = sizeof(ofn);
ofn.hwndOwner   = h_main;
ofn.lpstrFile   = LPWSTR(szFile);

// Set lpstrFile[0] to '\0' so that GetOpenFileName does not
// use the contents of szFile to initialize itself.
ofn.lpstrFile       = LPWSTR(szFile);
ofn.nMaxFile        = sizeof(szFile);
ofn.lpstrFilter     = TEXT("Text Files (*.txt)\0*.txt\0All Files (*.*)\0*.*\0");
ofn.nFilterIndex    = 1;
ofn.lpstrFileTitle  = NULL;
ofn.nMaxFileTitle   = 0;
ofn.lpstrInitialDir = NULL;
ofn.Flags           = OFN_PATHMUSTEXIST | OFN_FILEMUSTEXIST;


// Display the Open dialog box.
/*if (GetOpenFileName(&ofn) == TRUE) {
    hf = CreateFile(ofn.lpstrFile,
        GENERIC_READ,
        0,
        (LPSECURITY_ATTRIBUTES) NULL,
        OPEN_EXISTING,
        FILE_ATTRIBUTE_NORMAL,
        (HANDLE) NULL);
}*/

char filename[40] = "C:\\Users\\weylspinor\\Desktop\\test.avi";
CvCapture *G_movie_file = cvCaptureFromAVI(filename);

I'd appreciate it if anyone can point me to my error.

Cheers,
-J