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.
Create a new project in Visual Basic. Form1 is created by default.
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
Add a Text Box control to Form1. Text1 is created by default. Set its MultiLine property to True.
Add a Command Button control to Form1. Command1 is created by default.
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.
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