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Linux kernel and C library user-space interface documentation


POSIX Manual Pages


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.
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.








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 .
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