Are Visual Studio 6 typelibs handled differently in Visual Studio 2008 under Vista and 7?

Question

I have written a standard DLL in Visual Studio 6 C++. I have also written a typelib to go with it so that it can be used directly in VB6 rather than via Declare.

It works fine in VB6 under Windows XP.

What doesn't work is when I take the DLL and the TLB into Vista and Windows7. There the .TLB registers fine with REGTLIB but the only symbol that is visible in Visual Studio 2008 is the Attribution constant.

The technique I'm attempting to emulate is found at How To Make C DLL More Accessible to VB with a Type Library. Is it the case that this technique no longer applies???

The (abbreviated) ODL code is reproduced below. Any idea what's going on?

// This is the type library for BOBDE.dll
[
    // Use GUIDGEN.EXE to create the UUID that uniquely identifies
    // this library on the user's system. NOTE: This must be done!!
    uuid(EE090BD0-AB6C-454c-A3D7-44CA46B1289F),
    // This helpstring defines how the library will appear in the
    // References dialog of VB.
    helpstring("BOBDE TypeLib"),
    // Assume standard English locale.  
    lcid(0x0409),
    // Assign a version number to keep track of changes.
    version(1.0)
]
library BOBDE
{
    // Now define the module that will "declare" your C functions.
[helpstring("Functions in BOBDE.DLL"), version(1.0),dllname("BOBDE.dll")]   
    module BOBDEFunctions
    {
[helpstring("Blowfish Encode ASCII for ANSI"), entry("BEA_A")] 
    void __stdcall BEA_A( [in] BSTR p1, [in] BSTR p2, [out,retval] BSTR* res );
    // other very similar functions removed for the sake of brevity
const LPSTR Attribution = "This product includes cryptographic software written by Eric Young ([email protected])"; 
    } // End of Module
}; // End of Library

Answer 1

The problem here is that you not just changed the operating system, you also changed your development tools. It should still work if you run VB6 on Win7. But Visual Studio 2008 supports VB.NET, a very different language from VB6. It only supports 'true' type libraries, the ones that COM uses.

Calling an exported function from a DLL requires using the P/Invoke marshaller built into .NET. Check out DllImportAttribute and the VB.NET Declare statement in the MSDN Library. The declaration for that function ought to resemble this:

<DllImport("bobde.dll")> _
Function BEA_A( _
      <MarshalAs(UnmanagedType.BStr)> ByVal p1 As String, _
      <MarshalAs(UnmanagedType.BStr)> ByVal p2 As String) _
    As <MarshalAs(UnmanagedType.BStr)> String
End Function

No need to register a type library with this. Writing a managed class wrapper in the C++/CLI language would be another approach.

Answer 2

Any reason you are creating typelib and not just declaring functions in VB6? Putting

Private Declare Function BEA_A Lib "bobde.dll" _
(ByVal p1 As String, ByVal p2 As String) As String 

at the top of your module seems a lot simpler.