I have two questions on this WSASocketA

1) Does anybody know where I can get the definition of GROUP type? Is it a structure?
2) And what's the size of member "g"? Is it a word, dword or anything?

Thanks in advance

In MSDN from 2008 (where there’s still information about Windows 9x compatibility) the parameter is specified just as reserved for all the OSes from Win95 up to Vista.

So, it seems, the parameter is just starting to be used and the public usage is not yet expected. It is plain unsigned int, i.e. platform-bitness-sized. Just pass zero on the stack.

Thanks, DimonSoft.

I think it is still a DWORD-sized on Win64, plus your confirmation. Since it's the 5th argument, the placement is on [rsp+32] and dwFlags (the 6th argument) should be on [rsp+36] above the shadow space and not [rsp+40] as I originally thought. If so, then these two members share the same stack 'unit' (they occupy only 8 bytes instead of 16), and I have to re-adjust my stack allocation to ensure the alignment is observed (sub rsp,40 instead of sub rsp,56).