sys_select.h(7POSIX) POSIX Programmer's Manual sys_select.h(7POSIX)
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.
sys/select.h — select types
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
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 applica‐
tions should ensure that the arguments they supply are never expressions with side-
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 <sig‐
nal.h> and <time.h>.
The following sections are informative.
<signal.h>, <sys_time.h>, <sys_types.h>, <time.h>
The System Interfaces volume of POSIX.1‐2008, pselect()
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 discrep‐
ancy 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 https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 sys_select.h(7POSIX)