CFormatDriveDialog - A wrapper class for the undocumented SHFormatDrive API function

• Download source - 2 Kb
• Download demo project - 21 Kb

Overview

This class basically brings up the Windows Disk-Format dialog box. You'd have thought it would have become part of the common dialogs by now. What's worse is that some of the information in KB article Q173688 is now incorrect as far as Windows XP and Windows 2000 are concerned. I presume that the KB article was written during the 9x days and they forgot to remove or update it later. What confused me was that the KB article  states that the information in it applies to XP and 2K. The first shock for me was to discover that the Quick-Format option behaved exactly opposite to how it was described in the KB article. In addition the Make-system-disk option was not even working properly. Anyway I've written a class - CFormatDriveDialog that basically wraps the stuff for you. I have stuck to the MS recommended constant definitions where they work, but in other cases I've either discarded them or added my own.

Strong warning

The information in KB article Q173688 is partially incorrect. Do not follow it blindly if you intend to build on this class. Also note that this class should only be used on Win2K/XP systems. The KB article is to be followed for older OS versions like 9x and ME.

Class Reference

There's just one public method here (of course, in addition to the parameter-less constructor).

DoModal

int CFormatDriveDialog::DoModal(HWND hWnd, UINT Drive, bool bQuickFormat, LPCTSTR vol_label);

• hWnd - The window handle of the dialog's parent. This cannot be NULL.
• Drive - The drive code (0 for A, 1 for B, 2 for C etc.) I've defined constants like DRIVEA, DRIVEB, DRIVEC etc. which you may use instead of raw numbers. They are defined in the header file.
• bQuickFormat - If true then the Quick-Format check box is ticked by default.
• vol_label - The default value for the volume label to be used.

Return Value

IDOK if a successful format was completed and IDCANCEL if the format operation was cancelled or if some error occurred.

Sample Usage

void Cnish_testDlg::OnBnClickedButton1()
{
    UpdateData(true);
    CFormatDriveDialog dlg;
    int d=dlg.DoModal(AfxGetMainWnd()->m_hWnd,DRIVEA,
        bQuickFormat,m_vollab);
    if(d==IDOK)
        MessageBox("yeah"); 
}

Tech Details

We call the SHFormatDrive function from shell32.dll. I use LoadLibrary and load shell32.dll and then call GetProcAddress to get SHFormatDrive's address. I also use SetWindowsHookEx to set a CBT hook because we need to set the volume label. The hook proc calls EnumChildWindows and when we encounter a child window with "Edit" class, we know this is the volume label edit box, because that's the only edit box in the dialog. Refer the source code for full details. A snipped partial listing is given below with comments not found in the actual source code.

int CFormatDriveDialog::DoModal(...)
{

    //...

    // Function pointer to hold SHFormatDrive
    FMTDRIVEFUNC* pshfd;

    // Load the dll
    HMODULE hMod = LoadLibrary("shell32.dll");

    // Chk for error - just in case
    if(hMod)
    {
        // Assign function pointer
        pshfd = reinterpret_cast<FMTDRIVEFUNC*>
            (GetProcAddress(hMod,"SHFormatDrive"));

        // Set a WH_CBT hook
        m_hHook = SetWindowsHookEx(WH_CBT,CBTProc,
            AfxGetApp()->m_hInstance,AfxGetApp()->m_nThreadID);

        // Call the function via the function pointer
        rv = ((*pshfd)(hWnd,Drive,SHFMT_ID_DEFAULT,Options)==
            SHFMT_FMTSUCCESS) ? IDOK : IDCANCEL;

        // Free the dll
        FreeLibrary(hMod);
    }
    
    //...
}

LRESULT CALLBACK CFormatDriveDialog::CBTProc(...)
{
    if (nCode == HCBT_ACTIVATE )
    { 
        // Get handle of Format dialog
        HWND hWnd = reinterpret_cast<HWND>(wParam);

        // Enumerate all child windows to get 
        // volume label the edit box
        EnumChildWindows(hWnd,EnumChildProc,NULL); 

        // Finished our need for the hook
        UnhookWindowsHookEx(m_hHook);
        CFormatDriveDialog::m_hHook = NULL; 
    }
    return FALSE;
}

BOOL CALLBACK CFormatDriveDialog::EnumChildProc(...)
{ 
    char buff[256];
    GetClassName(hwnd,buff,255);

    // The vol label edit box is the only edit control
    if(strcmp(buff,"Edit")==0)
    {
        SetWindowText(hwnd,m_vol_label);
        return FALSE;
    }
    return TRUE;
}

Conclusion

There are several return codes and option codes mentioned in the above mentioned KB article. But none of them work as expected, and some of them don't work at all. In addition the code constant given for Quick-Format works in the exact opposite manner. Of course I base my results from trying out the code on my own machine which is an XP professional box. I also got James T Johnson to test it partially on his XP professional box and Smitha(Tweety) to test it on her Windows 2000 professional box. But I have no idea how this class will work on untested OS versions with or without service packs.