Open System Services System Calls Reference Manual (G06.28+, H06.05+)

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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 Guardian processes: system library

G-series native OSS processes: system library

H-series native Guardian processes: implicit libraries

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 range of open ﬁle descriptors that might be ready for reading or

writing or that have exceptions pending. The select() function tests ﬁle descrip-

tors in the range of 0 (zero) through nfds -1.

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

ﬁle descriptors to be checked for having exception conditions pending. Upon

return from a successful call, this ﬁle descriptor set speciﬁes ﬁle descriptors that

have exception conditions pending.

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