gera3323,
WSAStartup, getsockopt

MasterZivgera3323MasterZiv,

простите не уточнил.

IPv4, tcp, for windows

В TCP-то нет размера буфера...
Блин, я это чего такое ?
SO_RCVBUF int The total per-socket buffer space reserved for receives.
SO_SNDBUF int The total per-socket buffer space reserved for sends.
http://msdn.microsoft.com/en-us/library/windows/desktop/ms740476(v=vs.85).aspx

А какой еще смысл может иметь "размер буфера"?

http://msdn.microsoft.com/en-us/library/windows/desktop/ms738544(v=vs.85).aspx
Тут немножко интереснее:
SO_RCVBUF int The total per-socket buffer space reserved for receives. This is unrelated to SO_MAX_MSG_SIZE and does not necessarily correspond to the size of the TCP receive window.

SO_SNDBUF int The total per-socket buffer space reserved for sends. This is unrelated to SO_MAX_MSG_SIZE and does not necessarily correspond to the size of a TCP send window.
Судя по "does not necessarily correspond to the size of a TCP send/receive window", это не те буфера что описаны в RFC