[VB6] How Do I Get The CD ROM Drive Letter?

[HanneSThEGreaT]

Q: What APIs Are Needed In Order To Obtain The CD ROM Drive Letter On The System?

A: You will only need 2 APIs for this purpose :
GetDriveType
GetLogicalDriveStrings

You declare them like the following :

'Determines whether a disk drive is a removable, fixed, CD-ROM, RAM disk, or network drive
Private Declare Function GetDriveType Lib "kernel32" Alias "GetDriveTypeA" _
    (ByVal nDrive As String) As Long

'Fills a buffer with strings that specify valid drives in the system.
Private Declare Function GetLogicalDriveStrings Lib "kernel32" _
    Alias "GetLogicalDriveStringsA" _
    (ByVal nBufferLength As Long, ByVal lpBuffer As String) As Long

Const DRIVE_CDROM& = 5 'Signifies CD ROM

Q: How do I actually use these APIs, In Other Words, How Do We Implement Them?

A: We will need to create a Function / Sub procedure to basically translate the GetLogicalDriveStrings API's return value, so that we can understand it properly, and provide the correct output to the user, in an understandable way :

Public Function GetDriveStrings() As String

    ' Wrapper for calling the GetLogicalDriveStrings api
    
    Dim result As Long          ' Result of our API calls
    Dim strDrives As String     ' String to pass to API call
    Dim lenStrDrives As Long    ' Length of the above string
    
    ' Call GetLogicalDriveStrings with a buffer size of zero to
    ' find out how large our stringbuffer needs to be
    result = GetLogicalDriveStrings(0, strDrives)
    
    strDrives = String(result, 0)
    lenStrDrives = result
    
    ' Call again with our new buffer
    result = GetLogicalDriveStrings(lenStrDrives, strDrives)
    
    If result = 0 Then
        ' There was some error calling the API
        ' Pass back an empty string
        ' NOTE - TODO: Implement proper error handling here
        GetDriveStrings = ""
    Else
        GetDriveStrings = strDrives
    End If
    
End Function

Q: IS That All?

A: Nope. Now that we have the correct converted output, we still need to inform the user. The next segment firstly ascertains whether or not a CD ROM exists on the system, then provides us with its Drive letter..

Private Sub Command1_Click()

    Dim strDrives As String
    Dim blnDrive As Boolean
    
    ' Find out what drives we have on this machine
    strDrives = GetDriveStrings()
    
    If strDrives = "" Then
        ' No drives were found
        MsgBox "No Drives were found!", vbCritical
    Else
        ' Walk through the string and check the type of each drive
        ' displaying any cd-rom drives we find
        Dim pos As Long
        Dim drive As String
        Dim drivetype As Long
        
        pos = 1
        
        Do While Not Mid$(strDrives, pos, 1) = Chr(0)
            drive = Mid$(strDrives, pos, 3)
            pos = pos + 4
            
            drivetype = GetDriveType(drive)
            
            If drivetype = DRIVE_CDROM Then
                    blnDrive = True
            Else
                    blnDrive = False
                
            End If
        Loop
        
        If blnDrive Then
            MsgBox "CD-ROM found at drive " & UCase(drive)
        Else
            MsgBox "No CD ROM found!"
        End If

    End If
    
End Sub

A full working sample is attached to this post.