Select (Unix)
select is a system call and application programming interface (API) in Unix-like and POSIX-compliant operating systems for examining the status of file descriptors of open input/output channels. The select system call is similar to the "poll" facility introduced in UNIX System V and later operating systems. However, with the c10k problem, both select and poll have been superseded by the likes of kqueue, epoll, /dev/poll and I/O completion ports. One common use of select outside of its stated use of waiting on filehandles is to implement a portable sub-second sleep. This can  be achieved by passing NULL for all three fd_set arguments, and the duration of the desired sleep as the timeout argument. In the C programming language, the select system call is declared in the header file sys/select.h or unistd.h, and has the following syntax: int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *timeout); codice_1 arguments may be manipulated with four utility macros: FD_SET(), FD_CLR(), FD_ZERO(), and FD_ISSET(). Select returns the total number of bits set in readfds, writefds and errorfds, or zero if the timeout expired, and -1 on error. The sets of file descriptor used  in select are finite in size, depending on the operating system. The newer system call "poll" provides a more flexible solution. Example. /* function prototypes */ void die(const char*); int main(int argc, char **argv) void die(const char *msg)