HOWTO: Call SHFormatDrive in Windows 95 and Windows NT
Ripped by -=Assarbad=-

The information in this article applies to:
  • Microsoft Win32 Application Programming Interface (API)


Although most Win32 applications do not need to be able to format disks, some do. Windows 95 and Windows NT provide an API function called SHFormatDrive, which presents the same dialog box as the Windows 95 and Windows NT shells, formats the specified diskette. This article describes how to call SHFormatDrive.


Currently, SHFormatDrive is not in the Platform SDK documentation or SHELLAPI.H. However, it is in SHELL32.LIB. Until the documentation and SHELLAPI.H are updated, use the following declarations and function description:

   #if !defined(SHFMT_OPT_FULL)

   #if defined (__cplusplus)
   extern "C" {

   The SHFormatDrive API provides access to the Shell's format
   dialog box. This allows applications that want to format disks to bring
   up the same dialog box that the Shell uses for disk formatting.

      hwnd    = The window handle of the window that will own the
        dialog. NOTE that hwnd == NULL does not cause this
        dialog to come up as a "top level application"
        window. This parameter should always be non-null,
        this dialog box is only designed to be the child of
        another window, not a stand-alone application.

      drive   = The 0 based (A: == 0) drive number of the drive
        to format.

      fmtID   = Currently must be set to SHFMT_ID_DEFAULT.

      options = There are currently only two option bits defined.


        SHFMT_OPT_FULL specifies that the "Quick Format"
        setting should be cleared by default. If the user
        leaves the "Quick Format" setting cleared, then a
        full format will be applied (this is useful for
        users that detect "unformatted" disks and want
        to bring up the format dialog box).

        If options is set to zero (0), then the "Quick Format"
        setting is set by default. In addition, if the user leaves
        it set, a quick format is performed. Under Windows NT 4.0,
        this flag is ignored and the "Quick Format" box is always
        checked when the dialog box first appears. The user can
        still change it. This is by design.

        The SHFMT_OPT_SYSONLY initializes the dialog to
        default to just sys the disk.

        All other bits are reserved for future expansion
        and must be 0.

        Please note that this is a bit field and not a
        value, treat it accordingly.

     The return is either one of the SHFMT_* values, or if
     the returned DWORD value is not == to one of these
     values, then the return is the physical format ID of the
     last successful format. The LOWORD of this value can be
     passed on subsequent calls as the fmtID parameter to
     "format the same type you did last time".

   DWORD WINAPI SHFormatDrive(HWND hwnd,
                  UINT drive,
                  UINT fmtID,
                  UINT options);

   // Special value of fmtID which means "use the defaultformat"

   #define SHFMT_ID_DEFAULT   0xFFFF

   // Option bits for options parameter

   #define SHFMT_OPT_FULL     0x0001
   #define SHFMT_OPT_SYSONLY  0x0002

   // Special return values. PLEASE NOTE that these are DWORD values.

   #define SHFMT_ERROR     0xFFFFFFFFL    // Error on last format,
                      // drive may be formatable
   #define SHFMT_CANCEL    0xFFFFFFFEL    // Last format wascanceled
   #define SHFMT_NOFORMAT  0xFFFFFFFDL    // Drive is not formatable

   #if defined (__cplusplus)
Here is an example call to SHFormatDrive that will format a diskette in drive "A:".
   SHFormatDrive (hMainWnd, 0 /* A: */, SHFMT_ID_DEFAULT, 0);
Normally, if a diskette is not in the drive when SHFormatDrive is called, the system displays a critical error dialog box that asks the user to Abort, Retry, or Ignore. You can prevent the system from displaying this dialog box by calling the SetErrorMode API with SEM_FAILCRITICALERRORS. If the application has already set this flag, the critical error dialog box will not appear. If you want this dialog box to appear, use the following code:
   UINT OldMode = SetErrorMode(0); // Get the current Error Mode settings.
   SetErrorMode(OldMode & !SEM_FAILCRITICALERRORS); // Force O/S to handle
                            //critical errors.
   // Call SHFormatDrive here.
   SetErrorMode(OldMode); // Put it back the way it was.

Delphi implementation

   // Option bits for options parameter
  SHFMT_OPT_FULL = $0001;

  SHFMT_ERROR = $FFFFFFFF; // Error on last format, drive may be formatable
  SHFMT_CANCEL = $FFFFFFFE; // Last format wascanceled
  SHFMT_NOFORMAT = $FFFFFFFD; // Drive is not formatable

function SHFormatDrive(hwnd, drive, fmtID, options: Cardinal): LongWord; stdcall; external 'shell32.dll';

Last Reviewed: July 9, 2000 [ripped 19.09.2001]
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Original files: HOWTO: Call SHFormatDrive in Windows 95 and Windows NT