Which type library hosts stdDataFormat?

Question

I am trying to import VB6's VBRUN type library into a Visual C++ 2017 header file, but it is failing due to a missing dependency.

Visual C++ reports

"error C4772: #import referenced a type from a missing type library; 'missing_type' used as a placeholder"

Viewing the file with OLE View reveals the problem is with the DataFormat property (DataFormat([out, retval] --** Return)).

The missing dependency would appear to be stdDataFormat: which type library does stdDataFormat reside in and why is it missing? (My operating system is Windows 10 Enterprise, 21H1.) Did I miss a selection when installing Visual Studio 6?

user_3195477 · Answer

This addresses the first part of the question, how to find the typelib (TLB) containing a given interface or class.

Assuming you have no preconception about the TLB / DLL hosting a given COM interface or class you can find it by a couple of registry searches, assuming the type in question actually has been registered.

I started off in HKEY_CLASSES_ROOT with a search for data values = stdDataFormat. This lead to:

[HKEY_CLASSES_ROOT\MSSTDFMT.StdDataFormat]
@="StdDataFormat Object"

[HKEY_CLASSES_ROOT\MSSTDFMT.StdDataFormat\CLSID]
@="{6D835690-900B-11D0-9484-00A0C91110ED}"

Now armed with the CLSID GUID of 6D835690-900B-11D0-9484-00A0C91110ED, search for that value, finding:

HKEY_CLASSES_ROOT\WOW6432Node\CLSID\{6D835690-900B-11D0-9484-00A0C91110ED

of which its important sub-element for our purposes is:

[HKEY_CLASSES_ROOT\WOW6432Node\CLSID\{6D835690-900B-11D0-9484-00A0C91110ED}\InprocServer32]
@="c:\windows\SysWow64\msstdfmt.dll"
...

The InprocServer32 value was the main thing I wanted to find; it tells you the DLL - which is c:\windows\SysWow64\msstdfmt.dll (on my PC - but this should be typical).

Opening msstdfmt.dll in OLEView (or OLEViewDotNet) confirms this; the decompiled IDL from the TLB in that DLL contains:

[
  uuid(6D835690-900B-11D0-9484-00A0C91110ED),
  helpstring("StdDataFormat Object"),
  helpcontext(0x00066b5f)
]
coclass StdDataFormat {
    [default] interface IStdDataFormatDisp;
    [default, source] dispinterface IStdDataFormatEvents;
};

So msstdfmt.dll should be the missing dependency.

If you did suspect this DLL to begin with, then obviously its a lot quicker to just load it in OLEView and check. But in many cases that won't be obvious when you're starting out.

As for the second part of the question - why is this dependency missing - maybe it would help if you added the relevant section of your code / includes?

Which type library hosts stdDataFormat?

1 Answers