How To Determine File Type from Registered CLSID

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Article ID: 174050 - View products that this article applies to.
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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

The following example creates a Visual Basic project that shows how to retrieve and use the CLSID associated with a given file. Constants are only defined for two versions of Microsoft Excel and two versions of Microsoft Word to demonstrate this technique. This example can be modified to work for any file format with a unique CLSID associated with it.

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 Standard EXE project. Form1 is created by default.
  2. Add a Command button, a TextBox, and two Labels to Form1.
  3. 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
    
          Private Sub Form_Load()
                     Label1.AutoSize = True
                     Label2.AutoSize = True
                End Sub
    
    						
  4. Add a Module to the project. In Visual Basic 4, choose "Module" from the "Insert" menu. In later versions of Visual Basic, choose "Add Module" from the "Project" menu.
  5. 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
    
    						
  6. 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)

Properties

Article ID: 174050 - Last Review: July 16, 2004 - Revision: 3.2
APPLIES TO
  • Microsoft Visual Basic 6.0 Learning Edition
  • Microsoft Visual Basic 6.0 Professional Edition
  • Microsoft Visual Basic 6.0 Enterprise Edition
  • Microsoft Visual Basic 5.0 Control Creation Edition
  • Microsoft Visual Basic 5.0 Learning Edition
  • Microsoft Visual Basic 5.0 Professional Edition
  • Microsoft Visual Basic 5.0 Enterprise Edition
  • Microsoft Visual Basic 4.0 Standard Edition
  • Microsoft Visual Basic 4.0 Professional Edition
  • Microsoft Visual Basic 4.0 32-Bit Enterprise Edition
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