DLGINIT is a pseudoresource used for initialization of ActiveX controls with MFC and ATL in C++ (or other object oriented languages).
It is handled dynamically in the MFC high level dialog classes. For a description see
here.
A definition of the DLGINIT structure can be found in
'atlhost.h'.
I don't understood which use you want do in C, but it should be possible to create a fake DLGINIT using a custom resource and the layout and values showed in atlhost.h