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.
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
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
The <sys/select.h> header shall define the following symbolic
constant, which shall have a value suitable for use in #if
FD_SETSIZE Maximum number of file descriptors in an fd_set
The following shall be declared as functions, defined as macros, or
both. If functions are declared, function prototypes shall be
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.
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 http://www.unix.org/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
IEEE/The Open Group 2013 sys_select.h(0P)