How to define a struct data interface in a ActiveX control?

I hope define a struct interface as GetPostInfo(PostInfo* postinfo); in a ActiveX control,

for example this struct as following:
typedef Struct PostInfo
{
   long nIndex;
   BSTR strPostName;
} PostInfo
 
and how to define that parameter of a FUNCTION definition in a xxxctrl.h
DISP_FUNCTION(CxxxCtrl, "GetPostInfo", GetPostInfo, VT_BOOL, ?)

so I must define this PostInfo struct in ODL file, and I hope this interface as a common data type, for example DRAWITEMSTRUCT, the data can be transfer from COM inside to user.