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SELECT(2) System Calls Manual SELECT(2) NAME select, FD_CLR, FD_ISSET, FD_SET, FD_ZERO - synchronous I/O multiplex- ing SYNOPSIS #include <sys/select.h> int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *timeout) void FD_CLR(int fd, fd_set *fdset) int FD_ISSET(int fd, fd_set *fdset) void FD_SET(int fd, fd_set *fdset) void FD_ZERO(fd_set *fdset) DESCRIPTION Select examines the file descriptors given in the sets readfds, writefds, and errorfds, up to and including file descriptor nfds-1 , for reading, writing, or exceptional conditions, respectively. Select currently supports regular files, pipes, named pipes, sockets, and character devices. If the readfds argument is not a null pointer, it points to an object of type fd_set that on input specifies the file descriptors to be checked for being ready to read, and on output indicates which file de- scriptors are ready to read. Writefds and errorfds have an analogous meaning for file descriptors to be checked for being ready to read, re- spectively have pending exceptional (error) conditions. 4th Berkeley Distribution Jun 9, 2005 SELECT(2)