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sys/select.h - select types
The <sys/select.h> header shall define the timeval structure that
includes at least the following members:
time_t tv_sec Seconds.
suseconds_t tv_usec Microseconds.
The time_t and suseconds_t types shall be defined as described in
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
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
void FD_ZERO(fd_set *fdset)
Initializes the file descriptor set fdset to have zero bits for
all file descriptors.
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 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 <signal.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 original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .