close.2

Unix操作系统minix 2.0源码

.\" Copyright (c) 1980 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)close.2	6.3 (Berkeley) 5/22/86
.\"
.TH CLOSE 2 "May 22, 1986"
.UC 4
.SH NAME
close \- delete a descriptor
.SH SYNOPSIS
.nf
.ft B
#include <unistd.h>

int close(int \fId\fP)
.ft R
.fi
.SH DESCRIPTION
The
.B close
call deletes a descriptor from the per-process object
reference table.
If this is the last reference to the underlying object, then
it will be deactivated.
For example, on the last close of a file
the current \fIseek\fP pointer associated with the file is lost;
on the last close of a TCP/IP descriptor
associated naming information and queued data are discarded;
on the last close of a file holding an advisory lock
the lock is released (see further
.BR fcntl (2)).
.PP
A close of all of a process's descriptors is automatic on
.IR exit ,
but since
there is a limit on the number of active descriptors per process,
.B close
is necessary for programs that deal with many descriptors.
.PP
When a process forks (see
.BR fork (2)),
all descriptors for the new child process reference the same
objects as they did in the parent before the fork.
If a new process is then to be run using
.BR execve (2),
the process would normally inherit these descriptors.  Most
of the descriptors can be rearranged with
.BR dup2 (2)
or deleted with
.B close
before the
.B execve
is attempted, but if some of these descriptors will still
be needed if the
.B execve
fails, it is necessary to arrange for them to be closed if the
.B execve
succeeds.
For this reason, the call ``fcntl(d, F_SETFD, \fIflags\fR)'' is provided,
that can be used to mark a descriptor "close on exec" by setting
the
.B FD_CLOEXEC
flag:
.PP
.RS
fcntl(d, F_SETFD, fcntl(d, F_GETFD) | FD_CLOEXEC);
.RE
.SH "RETURN VALUE
Upon successful completion, a value of 0 is returned.
Otherwise, a value of \-1 is returned and the global integer variable
.B errno
is set to indicate the error.
.SH ERRORS
.B Close
will fail if:
.TP 15
[EBADF]
\fID\fP is not an active descriptor.
.SH "SEE ALSO"
.BR open (2),
.BR pipe (2),
.BR execve (2),
.BR fcntl (2).