HOWTO: Determine File Type from Registered CLSID

• Microsoft Visual Basic Control Creation, Learning, Professional, and Enterprise Editions for Windows, version 5.0
• Microsoft Visual Basic Standard, Professional, and Enterprise Editions, 32-bit only, for Windows, version 4.0

SUMMARY

You can use the Windows API to retrieve the CLSID (class ID) associated with a given file and use this value to determine the product and version of its format.

MORE INFORMATION

The CLSID for a product or component can be found in the Windows Registry under HKEY_CLASSES_ROOT. For example:

   MyComputer\HKEY_CLASSES_ROOT\Excel.Sheet.8\CLSID

NOTE: In order to identify a file on a given system, the appropriate CLSID must be registered on the system running this code. Also, this sample does not include any error trapping, which should be added for any production use of this technique.

Step-by-Step Example

1. Start a new project. Form1 is created by default.

2. Add a Command button, a TextBox, and two Labels to Form1.

3. Set the AutoSize property of each Label to True.

4. Copy the following code into the Form's module:

         Private Sub Command1_Click()
         Dim FileCLSID As String
   

         FileCLSID = GetCLSID(Text1.Text)
         Label2.Caption = FileCLSID
         Select Case FileCLSID
           Case EXCEL97
             Label1.Caption = "Excel 97"
           Case EXCEL95
             Label1.Caption = "Excel 95"
           Case WORD97
             Label1.Caption = "Word 97"
           Case WORD95
             Label1.Caption = "Word 95"
           Case Else
             Label1.Caption = "Unknown File Version"
         End Select
         End Sub
   
   

5. Add a Module to the project. In Visual Basic 4, choose "Module" from the "Insert" menu. In Visual Basic 5, choose "Add Module" from the "Project" menu.

6. Copy the following code into Module1:

         Type GUID
           B(16) As Byte
         End Type
   
         Declare Function GetClassFile Lib "Ole32.DLL" (ByVal lpszFileName _
         As String, ByRef pclsid As GUID) As Long
   
         Declare Function StringFromGUID2 Lib "Ole32.DLL" (ByRef rguid _
         As GUID, ByVal lpsz As String, ByVal cbMax As Long) As Long
   
         Public Const EXCEL97 As String = _
            "{00020820-0000-0000-C000-000000000046}"
         Public Const EXCEL95 As String = _
            "{00020810-0000-0000-C000-000000000046}"
         Public Const WORD97 As String = _
            "{00020906-0000-0000-C000-000000000046}"
         Public Const WORD95 As String = _
            "{00020900-0000-0000-C000-000000000046}"
   
         Function GetCLSID(FileName As String) As String
            Dim g As GUID
            Dim RetVal As Long
            Dim strGUID As String
   
            RetVal = GetClassFile(StrConv(FileName, vbUnicode), g)
            strGUID = Space(255)
            RetVal = StringFromGUID2(g, strGUID, 255)
            strGUID = StrConv(strGUID, vbFromUnicode)
            If (InStr(strGUID, Chr(0)) > 0) Then
               strGUID = Left(strGUID, InStr(strGUID, Chr(0)) - 1)
            End If
            GetCLSID = strGUID
         End Function
   
   

7. Run the project and enter a path and filename for a Word 97 or Word 95 document, or an Excel 97 or Excel 95 Worksheet into Text1. Click on Command1 and the type of file will be displayed in Label1 and the actual CLSID will be displayed in Label2.

REFERENCES

For more information, please Search on the following topics in either the Win32 Programmer's Reference or The Microsoft Developer Network (MSDN) Library CD:

• GetClassFile
• StringFromGUID2
• CLSID (class ID)

Keywords          : vb432 VB4WIN vb5all vb5howto
Version           : WINDOWS:4.0,5.0
Platform          : WINDOWS
Issue type        : kbhowto