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       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.


       poll.h — definitions for the poll() function


       #include <poll.h>


       The  <poll.h>  header  shall define the pollfd structure, which shall include at least the
       following members:

           int    fd       The following descriptor being polled.
           short  events   The input event flags (see below).
           short  revents  The output event flags (see below).

       The <poll.h> header shall define the following type through typedef:

       nfds_t        An unsigned integer type used for the number of file descriptors.

       The implementation shall support one or more programming environments in which  the  width
       of  nfds_t  is  no  greater  than  the width of type long.  The names of these programming
       environments can be obtained using the confstr() function or the getconf utility.

       The <poll.h> header shall define the following symbolic constants, zero or more  of  which
       may be OR'ed together to form the events or revents members in the pollfd structure:

       POLLIN        Data other than high-priority data may be read without blocking.

       POLLRDNORM    Normal data may be read without blocking.

       POLLRDBAND    Priority data may be read without blocking.

       POLLPRI       High priority data may be read without blocking.

       POLLOUT       Normal data may be written without blocking.

       POLLWRNORM    Equivalent to POLLOUT.

       POLLWRBAND    Priority data may be written.

       POLLERR       An error has occurred (revents only).

       POLLHUP       Device has been disconnected (revents only).

       POLLNVAL      Invalid fd member (revents only).

       The  significance  and  semantics of normal, priority, and high-priority data are file and

       The following shall be declared as a function and may  also  be  defined  as  a  macro.  A
       function prototype shall be provided.

           int   poll(struct pollfd [], nfds_t, int);

       The following sections are informative.








       The System Interfaces volume of POSIX.1‐2008, confstr(), poll()

       The Shell and Utilities volume of POSIX.1‐2008, getconf


       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2013 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX),  The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical  Corrigendum  1  applied.)  In  the  event of any
       discrepancy between this version and the original IEEE and The Open  Group  Standard,  the
       original  IEEE  and The Open Group Standard is the referee document. The original Standard
       can be obtained online at .

       Any typographical or formatting errors that appear in this page are most  likely  to  have
       been  introduced  during  the conversion of the source files to man page format. To report
       such errors, see .