can't make sense of LARGE_INTEGER struct

Question

With C++ and some Winapi things, I encountered this guy:

#if defined(MIDL_PASS)
typedef struct _LARGE_INTEGER {
#else // MIDL_PASS
typedef union _LARGE_INTEG         


        

Answer 1

You could directly access the LowPart and HighPart without having to go via the u member. As:

LARGE_INTEGER x;
x.HighPart = 42;

(Need to look up though if unnamed structs can be union members in Standard C.)

Answer 2

Microsoft provides anonymous structs as an extension (their example shows one struct inside another struct, but a struct in a union is similar). If you don't mind non-portable code based on their extension, you can use things like:

LARGE_INTEGER a;
a.LowPart = 1;

but if you want portable code, you need:

a.u.LowPart = 1;

The union lets you use either.