* VB-CODE (1)
Tip 149: Enumerating Disk Drives in Visual Basic 4.0

August 31, 1995

Abstract
When you write a program in Microsoft? Visual Basic?, you may need to
determine which disk drives are installed in the computer system. This
article shows how to enumerate all disk drives within Visual Basic
version 4.0.

Using the GetLogicalDriveString Function
You can use the Microsoft? Windows? application programming interface
(API) GetLogicalDriveString function in a Microsoft Visual Basic? program
to find out which disk drives are available. To use this function, you
must include the following Declare statement in the General Declarations
section of your program:

Private Declare Function GetLogicalDriveStrings Lib "kernel32" Alias
   "GetLogicalDriveStringsA" (ByVal nBufferLength As Long,
    ByVal lpBuffer As String) As Long

The GetLogicalDriveString function requires two arguments, as follows:

nBufferLength  A long value containing the maximum size of the lpBuffer
lpBuffer       A string buffer that will hold the drive letters

After the program calls this function, the lpBuffer is filled with
entries that describe each valid disk drive found in the computer
system. The string is null-terminated. Each entry in this string
contains the drive letter, followed by a colon and a backslash
character. For example, if drive A is found, the string will contain
the entry:

    NULL a:\ NULL NULL

Notice that each entry is terminated by a null byte, and the last entry
in the string is terminated by two consecutive null bytes.

The example program below displays a list of all available disk drives
in the Text Box control. The program uses the InStr and Mid functions
to extract each individual entry from the lpBuffer string.

Example Program
This program shows how to create a list of all disk drives installed in
the computer system.

 1. Create a new project in Visual Basic. Form1 is created by default.
 2. Add the following Declare statement to the General Declarations
    section of Form1 (note that this Declare statement must be typed
    as a single line of code):

Private Declare Function GetLogicalDriveStrings Lib "kernel32" Alias
   "GetLogicalDriveStringsA" (ByVal nBufferLength As Long,
   ByVal lpBuffer As String) As Long

 1. Add a Text Box control to Form1. Text1 is created by default. Set its
    MultiLine property to True.
 2. Add a Command Button control to Form1. Command1 is created by default.
 3. Add the following code to the Click event for Command1:

Private Sub Command1_Click()
    Dim X As Long
    Dim L As Integer
    Dim BufLen As Long
    Dim BufString As String * 256
    BufLen = 256
 
    Text1.Text = ""
    X = GetLogicalDriveStrings(BufLen, BufString)
    On Error GoTo Quit_Now
 
    Do
        X = Y + 1
        Z = Z + 1
        Y = InStr(X, BufString, "\")
        p$ = Mid$(BufString, Y - 2, 3)
        Text1.Text = Text1.Text & p$ & Chr$(13) & Chr$(10)

    Loop Until Y = 0
Quit_Now:
 
End Sub

Run the example program by pressing F5. Click the OK command button. The
Text Box will contain a list of all available disk drives in the computer
system.

Additional References
"GetLogicalDriveStrings." (Development Library, Product Documentation,
   SDKs, Win32 SDK, Win32 Programmer's Reference, Reference, Functions,
   GetFileTitle to GetMetaFileBits)