How To Call CLSID And ProgID Related COM APIs in Visual Basic

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Article ID: 183544 - View products that this article applies to.
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This article demonstrates how to use a set of related Component Object Model (COM) APIs that retrieve and manipulate CLSIDs and ProgIDs. The following APIs are discussed:
  • CLSIDFromProgID: To retrieve the CLSID of a COM object with a given ProgID.
  • StringFromCLSID: To convert a CLSID structure to a string.
  • CLSIDFromString: To convert a CLSID in string format to a structure.
  • ProgIDFromCLSID: To retrieve a ProgID with a given CLSID.


WARNING: One or more of the following functions are discussed in this article; VarPtr, VarPtrArray, VarPtrStringArray, StrPtr, ObjPtr. These functions are not supported by Microsoft Technical Support. They are not documented in the Visual Basic documentation and are provided in this Knowledge Base article "as is." Microsoft does not guarantee that they will be available in future releases of Visual Basic.
  1. Create a new ActiveX DLL project (Project1) in Visual Basic (Class1 is created by default).
  2. Compile the default project. Now, you have a test component: Project1.dll, which contains a COM class (Project1.Class1)
  3. Create a new Standard EXE project (Project1) in Visual Basic. Form1 is created by default.
  4. Add three TextBoxes, one Command button, and one ListBox to Form1.
  5. Add the following code to Form1's code module:
          ' ========== CODE FOR FORM1 ==============
          Option Explicit
          'CLSID/GUID structure
          Private Type GUID
              Data1 As Long
              Data2 As Integer
              Data3 As Integer
              Data4(7) As Byte
          End Type
          'API Declarations:
          Private Declare Function CLSIDFromProgID _
             Lib "ole32.dll" (ByVal lpszProgID As Long, _
             pCLSID As GUID) As Long
          Private Declare Function ProgIDFromCLSID _
             Lib "ole32.dll" (pCLSID As GUID, lpszProgID As Long) As Long
          Private Declare Function StringFromCLSID _
             Lib "ole32.dll" (pCLSID As GUID, lpszProgID As Long) As Long
          Private Declare Function CLSIDFromString _
             Lib "ole32.dll" (ByVal lpszProgID As Long, _
             pCLSID As GUID) As Long
          Private Declare Sub CopyMemory Lib "kernel32" Alias _
             "RtlMoveMemory" (pDst As Any, pSrc As Any, ByVal ByteLen As Long)
          Private Sub Command1_Click()
             Dim strProgID As String * 255
             Dim pProgID As Long
             Dim udtCLSID As GUID
             Dim strCLSID As String * 255
             Dim pCLSID As Long
             Dim lngRet As Long
             Dim strTemp As String
             Dim i As Integer
             'Take a ProgID.
             strTemp = Text1.Text
             'Get CLSID.
             lngRet = CLSIDFromProgID(StrPtr(strTemp), udtCLSID)
             'Display CLSID elements.
             With List1
                .AddItem Hex(udtCLSID.Data1)
                .AddItem Hex(udtCLSID.Data2)
                .AddItem Hex(udtCLSID.Data3)
                For i = 0 To 7
                   .AddItem Hex(udtCLSID.Data4(i))
             End With
             'Convert CLSID to a string and get the pointer back.
             lngRet = StringFromCLSID(udtCLSID, pCLSID)
             'Get the CLSID string and display it.
             StringFromPointer pCLSID, strCLSID
             Text2.Text = strCLSID
             'Reinitialize the CLSID.
             With udtCLSID
                .Data1 = 0
                .Data2 = 0
                .Data3 = 0
                For i = 0 To 7
                   .Data4(i) = 0
             End With
             'Convert the string back to CLSID.
             strTemp = Text2.Text
             lngRet = CLSIDFromString(StrPtr(strTemp), udtCLSID)
             'Get a pointer to ProgID string. This is a Unicode string.
             lngRet = ProgIDFromCLSID(udtCLSID, pProgID)
             'Get the ProgID and display it.
             StringFromPointer pProgID, strProgID
             Text3.Text = strProgID
          End Sub
          'This function takes a pointer to a Unicode string, a string buffer
          'and place the bytes in the Visual Basic string buffer.
          Private Sub StringFromPointer(pOLESTR As Long, strOut As String)
             Dim ByteArray(255) As Byte
             Dim intTemp As Integer
             Dim intCount As Integer
             Dim i As Integer
             intTemp = 1
             'Walk the string and retrieve the first byte of each WORD.
             While intTemp <> 0
                CopyMemory intTemp, ByVal pOLESTR + i, 2
                ByteArray(intCount) = intTemp
                intCount = intCount + 1
                i = i + 2
             'Copy the byte array to our string.
             CopyMemory ByVal strOut, ByteArray(0), intCount
          End Sub
          Private Sub Form_Load()
             Text1.Text = "Project1.Class1"
          End Sub
  6. Run the project, and press Command1. The following appears:
Text1: Displays the ProgID of the component that you want to get the CLSID from.
Text2: Displays the CLSID retrieved in string format.
Test3: Displays the ProgID retrieved based on the CLSID.
List1: Displays the members of the CLSID structure in hex format.


Article ID: 183544 - Last Review: March 11, 2005 - Revision: 3.2
  • Microsoft Visual Basic 5.0 Learning Edition
  • Microsoft Visual Basic 5.0 Professional Edition
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  • Microsoft Visual Basic 4.0 Professional Edition
  • Microsoft Visual Basic 4.0 32-Bit Enterprise Edition
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