<sys/select.h>(P) POSIX Programmer's Manual <sys/select.h>(P)
sys/select.h - select types
The <sys/select.h> header shall define the timeval structure that includes at least the
time_t tv_sec Seconds.
suseconds_t tv_usec Microseconds.
The time_t and suseconds_t types shall be defined as described in <sys/types.h> .
The sigset_t type shall be defined as described in <signal.h> .
The timespec structure shall be defined as described in <time.h> .
The <sys/select.h> header shall define the fd_set type as a structure.
Each of the following may be declared as a function, or defined as a macro, or both:
void FD_CLR(int fd, fd_set *fdset)
Clears the bit for the file descriptor fd in the file descriptor set fdset.
int FD_ISSET(int fd, fd_set *fdset)
Returns a non-zero value if the bit for the file descriptor fd is set in the file
descriptor set by fdset, and 0 otherwise.
void FD_SET(int fd, fd_set *fdset)
Sets the bit for the file descriptor fd in the file descriptor set fdset.
void FD_ZERO(fd_set *fdset)
Initializes the file descriptor set fdset to have zero bits for all file descrip-
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 defined as a macro:
Maximum number of file descriptors in an fd_set structure.
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>, <sys/time.h>, and <time.h>.
The following sections are informative.
<signal.h> , <sys/time.h> , <sys/types.h> , <time.h> , the System Interfaces volume of
IEEE Std 1003.1-2001, pselect(), select()
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 <sys/select.h>(P)