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

       sys/select.h — select types

SYNOPSIS

       #include <sys/select.h>

DESCRIPTION

       The <sys/select.h> header shall define the timeval structure, which shall include at least
       the following members:

           time_t         tv_sec      Seconds.
           suseconds_t    tv_usec     Microseconds.

       The <sys/select.h> header shall define the time_t and suseconds_t types  as  described  in
       <sys/types.h>.

       The <sys/select.h> header shall define the sigset_t type as described in <signal.h>.

       The <sys/select.h> header shall define the timespec structure as described in <time.h>.

       The <sys/select.h> header shall define the fd_set type as a structure.

       The <sys/select.h> header shall define the following symbolic constant, which shall have a
       value suitable for use in #if preprocessing directives:

       FD_SETSIZE  Maximum number of file descriptors in an fd_set structure.

       The following shall be declared as functions, defined as macros, or both. If functions are
       declared, function prototypes shall be provided.

           void FD_CLR(int, fd_set *);
           int  FD_ISSET(int, fd_set *);
           void FD_SET(int, fd_set *);
           void FD_ZERO(fd_set *);

       If  implemented  as  macros,  these  may  evaluate  their  arguments  more  than  once, so
       applications should ensure that the arguments they supply are never expressions with side-
       effects.

       The  following  shall be declared as functions and may also be defined as macros. Function
       prototypes shall be provided.

           int  pselect(int, fd_set *restrict, fd_set *restrict, fd_set *restrict,
                    const struct timespec *restrict, const sigset_t *restrict);
           int  select(int, fd_set *restrict, fd_set *restrict, fd_set *restrict,
                    struct timeval *restrict);

       Inclusion of the <sys/select.h> header may make  visible  all  symbols  from  the  headers
       <signal.h> and <time.h>.

       The following sections are informative.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       <signal.h>, <sys_time.h>, <sys_types.h>, <time.h>

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

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 .