PROLOG

       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.

NAME

       poll.h — definitions for the poll() function

SYNOPSIS

       #include <poll.h>

DESCRIPTION

       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
       device-specific.

       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.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       The System Interfaces volume of POSIX.1‐2017, confstr(), poll()

       The Shell and Utilities volume of POSIX.1‐2017, getconf

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1-2017, Standard for Information Technology -- Portable  Operating  System  Interface
       (POSIX),  The  Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by
       the Institute of Electrical and Electronics Engineers, Inc and The  Open  Group.   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 http://www.opengroup.org/unix/online.html .

       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 https://www.kernel.org/doc/man-pages/reporting_bugs.html .