FD_CLR - macros for synchronous I/O multiplexing
#include <sys/time.h> FD_CLR(int fd, fd_set *fdset); FD_ISSET(int fd, fd_set *fdset); FD_SET(int fd, fd_set *fdset); FD_ZERO(fd_set *fdset);
Refer to select().
<sys/time.h>.