Open System Services System Calls Reference Manual (G06.25+, H06.03+)

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System Functions (s and S) select(2)

NAME

select - Selects among ﬁle descriptors for synchronous input/output multiplexing

LIBRARY

G-series native OSS processes: system library

H-series OSS processes: implicit libraries

SYNOPSIS

#include <sys/time.h>

int select(

int nfds,

fd_set *readfds,

fd_set *writefds,

fd_set *errorfds,

struct timeval *timeout);

void FD_CLR(

int fd,

fd_set *fdset);

int FD_ISSET(

int fd,

fd_set *fdset);

void FD_SET(

int fd,

fd_set *fdset);

void FD_ZERO(

fd_set *fdset);

PARAMETERS

nfds Speciﬁes the number of open ﬁle descriptors that might be ready for reading or

writing or that have exceptions pending. The nfds parameter cannot be greater

than FD_SETSIZE.

readfds Points to a ﬁle descriptor set consisting of ﬁle descriptors of objects opened for

reading. When the function is called, this ﬁle descriptor set speciﬁes ﬁle descrip-

tors to be checked for being ready to read. Upon return from a successful call,

this ﬁle descriptor set speciﬁes ﬁle descriptors that are ready to be read.

writefds Points to a ﬁle descriptor set consisting of ﬁle descriptors for objects opened for

writing. When the function is called, this ﬁle descriptor set speciﬁes ﬁle descrip-

tors to be checked for being ready to write. Upon return from a successful call,

this ﬁle descriptor set speciﬁes ﬁle descriptors that are ready to be written.

errorfds Points to a ﬁle descriptor set consisting of ﬁle descriptors for objects opened for

reading or writing that have an exception pending. When the function is called,

this ﬁle descriptor set speciﬁes ﬁle descriptors to be checked for having error

conditions pending. Upon return from a successful call, this ﬁle descriptor set

speciﬁes ﬁle descriptors that have error conditions pending.

timeout Points to a type timeval structure that speciﬁes the time to wait for a response

from a call to the select() function. When the timeout parameter is not a null

pointer, the maximum time interval to wait for the select() function to ﬁnish is

speciﬁed by values stored in space reserved by the type timeval structure

pointed to by the timeout parameter.

The object pointed to by the timeout parameter can be modiﬁed after successful

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