How To Check for a Writeable Drive Under Windows NT (192304)


The information in this article applies to:

  • Microsoft Visual FoxPro for Windows 5.0
  • Microsoft Visual FoxPro for Windows 5.0a
  • Microsoft Visual FoxPro for Windows 6.0
This article was previously published under Q192304

SUMMARY

One way to check if a program is able to write to a drive is to attempt to create a temporary file on the drive. However, under Windows NT, this opens a system error dialog box if the drive is write-protected or otherwise not available to be written. This article demonstrates how to create and use the CheckMediaWrite() function to check if the drive is available for writing.

MORE INFORMATION

Using the SetErrorMode Win32 API function, a program can attempt to create a temporary file on a drive without raising an error on Windows NT if the drive is not available for writing.

Save the following code to a program file, place a write-protected disk in the floppy drive, and run the program.

Sample Code

   *-- Code begins here.
   CLEAR

   *-- Check if floppy drive a: is available for writing
   *-- and print the results.  Try this twice, once with
   *-- a write-protected floppy and again with a floppy
   *-- that is not write-protected.
   ? CheckMediaWrite("a:")

   *-----------------------------------------------------------------
   *- Function:    CheckMediaWrite
   *- Summary:     Checks if the passed drive is available for writing.
   *- Parameters:  lsDrive - The drive to check.
   *- Returns:     -1 If drive cannot be written to.
   *- Example:     liReturn = CheckWrite("a:")
   *-----------------------------------------------------------------
   FUNCTION CheckMediaWrite()
   PARAMETERS lsDrive

   *-- Defines from Winbase.h
   #DEFINE SEM_FAILCRITICALERRORS      0x0001
   #DEFINE SEM_NOGPFAULTERRORBOX       0x0002
   #DEFINE SEM_NOALIGNMENTFAULTEXCEPT  0x0004
   #DEFINE SEM_NOOPENFILEERRORBOX      0x8000

   *-- Check that the parameter is in the correct format.
   IF SUBSTR(lsDrive, 2, 1) <> ":" OR ;
     (ASC(UPPER(SUBSTR(lsDrive, 1, 1))) < 65 OR ;
     ASC(UPPER(SUBSTR(lsDrive, 1, 1))) > 90)
       =MESSAGEBOX("Drive must be in the format <drive letter>:", ;
         0, "Error")
       RETURN -1
   ENDIF

   *-- SetErrorMode determines whether the system handles
   *-- serious errors or whether the program handles them.
   DECLARE INTEGER SetErrorMode IN win32api INTEGER

   *-- SetErrorMode returns to what the flags were last set.
   *-- You need to store this in lnResult so that you can set them
   *-- back the way they were before calling SetErrorMode.
   *-- Failure to do so can produce unpredictable results
   *-- when encountering future errors.  SetErrorMode only
   *-- applies to the current process and therefore only affects
   *-- the FoxPro program that called SetErrorMode.
   lnResult = SetErrorMode(SEM_FAILCRITICALERRORS)

   hFile = FCREATE(lsDrive + "\tmp.txt")
   IF hFile <> -1
       FCLOSE(hFile)
       ERASE(lsDrive + "\tmp.txt")
   ENDIF

   *-- Put things back the way you found them.
   lnResult = SetErrorMode(lnResult)

   RETURN hFile
   *-- Code ends here.
A -1 appears on the desktop.

REFERENCES

(c) Microsoft Corporation 1998. All Rights Reserved. Contributions by Mike A. Stewart, Microsoft Corporation.
Modification Type:MinorLast Reviewed:6/29/2004
Keywords:kbcode kbhowto KB192304
©2004 Microsoft Corporation. All rights reserved.