ChDrive Procedure

ChDrive Procedure

Class

Microsoft.VisualBasic.FileSystem

Syntax

 ChDrive(   drive)

drive (required; String or Char): The letter of the drive (A-Z) to set as the new default drive

Description

Changes the current working (default) disk drive

Rules at a Glance

If a zero-length string is supplied, the drive is not changed.
If driveletter consists of more than one character, only the first character is used to determine the drive.

Example

The following example demonstrates a utility function that uses ChDrive to determine if a given drive is available. By centralizing the test, this reduces the amount of coding required each time you need to use ChDrive .

 Private Function IsAvailableDrive(sDrive As String) _                  As Boolean         'if an error occurs goto to the next line of code    On Error Resume Next         Dim sCurDrv As String         'get the letter of the current drive    sCurDrv = Left$(CurDir, 1)    'attempt to change the drive    ChDrive(sDrive)    'did an error occur?    If Err.Number = 0 Then       'no - this drive is OK to use       IsAvailableDrive = True    Else       'yes - don't use this drive       IsAvailableDrive = False    End If    'set the drive back to what it was    ChDrive(sCurDrv)          End Function

The following code snippet shows how this function could be implemented within your application:

 If IsAvailableDrive(sDrv) Then       ChDrive(sDrv)    Else       MsgBox ("Cannot use Drive " & sDrv & ":\")    End If

Programming Tips and Gotchas

The current directory is unaffected by the ChDrive procedure.
Since ChDrive only processes the first letter of the drive string, it's not possible to supply a piped name as a network drive name (for example, \\NTServer\ ). Instead, the machine on which your program runs must have a drive letter mapped to the network resource using Explorer or other network commands. If drive is specified as a UNC path , the function raises error number 5, "Invalid procedure call or argument," or generates an ArgumentException exception.
If drive is invalid, the function returns error number 68, "Device unavailable," or generates an IOException exception.
To determine which drive is current, call the CurDir function with no arguments. Then use the Left function to extract its first character, as the following code fragment illustrates:
```
 Dim sDrive As String = Left(CurDir(  ), 1) 
```

VB.NET/VB 6 Differences

In VB.NET, ChDrive is implemented as a procedure (a method of the FileSystem class). In VB 6, it is implemented as a statement. As a result, the VB.NET version requires parentheses around the drive argument.