The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### 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

> XSH confstr, poll

> XCU getconf

#### CHANGE HISTORY

> First released in Issue 4, Version 2.

#### Issue 6

> The description of the symbolic constants is updated to match the poll() function.

> Text related to STREAMS has been moved to the poll() reference page.

> A note is added to the DESCRIPTION regarding the significance and semantics of normal, priority, and high-priority data.

#### Issue 7

> The <poll.h> header is moved from the XSI option to the Base.

End of informative text.

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