Editing Drive Letter Assignments

The code example in this topic shows you how to add or remove persistent drive letter assignments. These drive letter assignments persist through system shutdown. For more information, see .

The code example uses the following functions: , , , and .

 

/* DLEDIT -- Drive Letter Assignment Editor Platforms: This program requires Windows 2000 or later. Command-line syntax: DLEDIT <drive letter> <device name> -- Adds a drive letter DLEDIT -r <drive letter> -- Removes a drive letter Command-line examples: If E: refers to the CD-ROM drive, use the following commands to make F: point to the CD-ROM drive instead. DLEDIT -r E:\ DLEDIT F:\ \Device\CdRom0 *****************************************************************
        WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
           This program will change drive letter assignments, and the
           changes persist through reboots. Do not remove drive letters
           of your hard disks if you do not have this program on floppy
           disk or you might not be able to access your hard disks
        *****************************************************************
        */
        #ifdef _WIN32_WINNT
        #undef _WIN32_WINNT
        #define _WIN32_WINNT 0x0500
        #endif
        #ifdef NTDDI_VERSION
        #undef NTDDI_VERSION
        #define NTDDI_VERSION 0x05000000
        #endif
        #include <Windows.h>
        #include <stdio.h>
        #include <tchar.h>
        #if defined (DEBUG)
           static void DebugPrint (LPCTSTR pszMsg, DWORD dwErr);
           #define DEBUG_PRINT(pszMsg, dwErr) DebugPrint(pszMsg, dwErr)
        #else
           #define DEBUG_PRINT(pszMsg, dwErr) NULL
        #endif
        #pragma warning (disable : 4800)
        void PrintHelp (LPCTSTR pszAppName);
        /*--------------------------------------------------------------------
        The main function is the main routine. It parses the command-line
        arguments and either removes or adds a drive letter.
        Parameters
           argc
              Count of the command-line arguments
           argv
              Array of pointers to the individual command-line arguments
        --------------------------------------------------------------------*/
        void _tmain (int argc, TCHAR *argv[])
        {
           TCHAR * pszDriveLetter,
                * pszNTDevice,
                * pszOptions;
           TCHAR szUniqueVolumeName[MAX_PATH];
           TCHAR szDriveLetterAndSlash[4];
           TCHAR szDriveLetter[3];
           BOOL fRemoveDriveLetter;
           BOOL fResult;
           if (argc != 3)
           {
              PrintHelp(argv[0]);
              return;
           }
           // Use the command line to see if user wants to add or remove the
           // drive letter. Do this by looking for the -r option.
           fRemoveDriveLetter = !lstrcmpi (argv[1], TEXT("-r"));
           if (fRemoveDriveLetter)
           {
              // User wants to remove the drive letter. Command line should
              // be: dl -r <drive letter>
              pszOptions = argv[1];
              pszDriveLetter = argv[2];
              pszNTDevice = NULL;
           }
           else
           {
              // User wants to add a drive letter. Command line should be:
              // dl <drive letter> <NT device name>
              pszOptions = NULL;
              pszDriveLetter = argv[1];
              pszNTDevice = argv[2];
           }
           // GetVolumeNameForVolumeMountPoint, SetVolumeMountPoint, and
           // DeleteVolumeMountPoint require drive letters to have a trailing
           // backslash. However, DefineDosDevice requires that the trailing
           // backslash be absent. So, use:
           //
           // szDriveLetterAndSlash for the mounted folder functions
           // szDriveLetter for DefineDosDevice
           //
           // This way, command lines that use a: or a:\
           // for drive letters can be accepted without writing back to the original command-
           // line argument.
           szDriveLetter[0] = pszDriveLetter[0];
           szDriveLetter[1] = TEXT(':');
           szDriveLetter[2] = TEXT('\0');
           szDriveLetterAndSlash[0] = pszDriveLetter[0];
           szDriveLetterAndSlash[1] = TEXT(':');
           szDriveLetterAndSlash[2] = TEXT('\\');
           szDriveLetterAndSlash[3] = TEXT('\0');
           // Now add or remove the drive letter.
           if (fRemoveDriveLetter)
           {
              fResult = DeleteVolumeMountPoint (szDriveLetterAndSlash);
              if (!fResult)
                 _tprintf(TEXT("error %lu: couldn't remove %s\n"),
                        GetLastError(), szDriveLetterAndSlash);
           }
           else
           {
              // To add a drive letter that persists through reboots, use
              // SetVolumeMountPoint. This requires the volume GUID path
              // of the device to which the new drive letter will refer.
              // To get the volume GUID path, use
              // GetVolumeNameForVolumeMountPoint; it requires the drive
              // letter to already exist. So, first define the drive
              // letter as a symbolic link to the device name. After
              // you have the volume GUID path the new drive letter will
              // point to, you must delete the symbolic link because the
              // mount manager allows only one reference to a device at a
              // time (the new one to be added).
              fResult = DefineDosDevice (DDD_RAW_TARGET_PATH, szDriveLetter,
                                         pszNTDevice);
              if (fResult)
              {
                  // If GetVolumeNameForVolumeMountPoint fails, then
                  // SetVolumeMountPoint will also fail. However,
                  // DefineDosDevice must be called to remove the temporary symbolic link.
                  // Therefore, set szUniqueVolume to a known empty string.
                 if (!GetVolumeNameForVolumeMountPoint (szDriveLetterAndSlash,
                          szUniqueVolumeName,
                          MAX_PATH))
                 {
                    DEBUG_PRINT(TEXT("GetVolumeNameForVolumeMountPoint failed"),
                                GetLastError());
                    szUniqueVolumeName[0] = '\0';
                 }
                 fResult = DefineDosDevice (
                              DDD_RAW_TARGET_PATH|DDD_REMOVE_DEFINITION|
                              DDD_EXACT_MATCH_ON_REMOVE, szDriveLetter,
                              pszNTDevice);
                 if (!fResult)
                    DEBUG_PRINT(TEXT("DefineDosDevice failed"),
                                GetLastError());
                 fResult = SetVolumeMountPoint (szDriveLetterAndSlash,
                                szUniqueVolumeName);
                 if (!fResult)
                    _tprintf (TEXT("error %lu: could not add %s\n"),
                              GetLastError(),
                            szDriveLetterAndSlash);
              }
           }
        }
        /*-------------------------------------------------------------------
        The PrintHelp function prints the command-line usage help.
        Parameters
           pszAppName
              The name of the executable. Used in displaying the help.
        -------------------------------------------------------------------*/
        void PrintHelp (LPCTSTR pszAppName)
        {
           _tprintf(
               TEXT("Adds/removes a drive letter assignment for a device.\n\n"));
           _tprintf(
               TEXT("Usage: %s   add a drive letter\n"), pszAppName);
           _tprintf(
               TEXT(" %s -r  remove a drive letter\n\n"), pszAppName);
           _tprintf(
               TEXT("Example: %s e:\\ \\Device\\CdRom0\n"), pszAppName);
           _tprintf(
               TEXT(" %s -r e:\\\n"), pszAppName);
        }
        #if defined (DEBUG)
        /*--------------------------------------------------------------------
        The DebugPrint function prints a string to STDOUT.
        Parameters
           pszMsg
              The string to be printed to STDOUT.
           dwErr
              The error code; usually obtained from GetLastError. If dwErr is
              zero, no error code is added to the error string. If dwErr is
              nonzero, the error code will be printed in the error string.
        --------------------------------------------------------------------*/
        void DebugPrint (LPCTSTR pszMsg, DWORD dwErr)
        {
           if (dwErr)
              _tprintf(TEXT("%s: %lu\n"), pszMsg, dwErr);
           else
              _tprintf(TEXT("%s\n"), pszMsg);
        }
        #endif