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 However, with the c10k problem, both select and poll have been superseded by the likes of kqueue, epoll, and I/O completion ports. 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:
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| - Select (Unix) (en)
- Select (Unix) (zh)
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| - select是用于I/O多路转接的一个系统调用函数。 在C程序中,该系统调用在 sys/select.h 或 unistd.h 中声明,语法如下: int select(int nfds, fd_set* readfds, fd_set* writefds, fd_set* errorfds, struct timeval* timeout); 为了维护fd_set类型的参数,会使用下面四个宏:FD_SET, FD_CLR, FD_ZERO 和 FD_ISSET。 返回值: 这个函数将返回描述符集的个数, 如果返回为0,错误则返回-1。 参看:
* select(2)
* poll(2) (zh)
- 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 However, with the c10k problem, both select and poll have been superseded by the likes of kqueue, epoll, and I/O completion ports. 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: (en)
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| - 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 However, with the c10k problem, both select and poll have been superseded by the likes of kqueue, epoll, and I/O completion ports.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); fd_set type 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. (en)
- select是用于I/O多路转接的一个系统调用函数。 在C程序中,该系统调用在 sys/select.h 或 unistd.h 中声明,语法如下: int select(int nfds, fd_set* readfds, fd_set* writefds, fd_set* errorfds, struct timeval* timeout); 为了维护fd_set类型的参数,会使用下面四个宏:FD_SET, FD_CLR, FD_ZERO 和 FD_ISSET。 返回值: 这个函数将返回描述符集的个数, 如果返回为0,错误则返回-1。 参看:
* select(2)
* poll(2) (zh)
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