IErrorInfo::GetSource method (oaidl.h)
Returns the language-dependent programmatic ID (ProgID) for the class or application that raised the error.
HRESULT GetSource( [out] BSTR *pBstrSource );
A ProgID, in the form progname.objectname.
If this method succeeds, it returns S_OK. Otherwise, it returns an HRESULT error code.
Use IErrorInfo::GetSource to determine the class or application that is the source of the error. The language for the returned ProgID depends on the locale ID (LCID) that was passed into the method at the time of invocation.