Four macros are defined in the header file Winsock2.h for manipulating
and checking the descriptor sets. The variable FD_SETSIZE determines the
maximum number of descriptors in a set. (The default value of
FD_SETSIZE is 64, which can be modified by defining FD_SETSIZE to
another value before including Winsock2.h.) Internally, socket handles
structure are not represented as bit flags as in Berkeley Unix. Their
data representation is opaque. Use of these macros will maintain
software portability between different socket environments. The macros
to manipulate and check
fd_set contents are:
FD_ZERO(*set) - Initializes set to the empty set. A set should always be cleared before using.
FD_CLR(s, *set) - Removes socket s from set.
FD_ISSET(s, *set) - Checks to see if s is a member of set and returns TRUE if so.