Q192304: HOWTO: Check for a Writeable Drive Under Windows NT

Article: Q192304
Product(s): Microsoft FoxPro
Version(s): WINDOWS:5.0,5.0a,6.0
Operating System(s): 
Keyword(s): 
Last Modified: 14-AUG-1999

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 5.0, 5.0a, 6.0 
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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.


Additional query words: kbVFp600 kbVFp500a kbVFp500 kbAPI

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Keywords          :  
Technology        : kbVFPsearch kbAudDeveloper kbVFP500 kbVFP600 kbVFP500a
Version           : WINDOWS:5.0,5.0a,6.0
Issue type        : kbhowto

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