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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "CLOSE" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" close 
.SH NAME
close \- close a file descriptor
.SH SYNOPSIS
.LP
\fB#include <unistd.h>
.br
.sp
int close(int\fP \fIfildes\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
The \fIclose\fP() function shall deallocate the file descriptor indicated
by \fIfildes\fP. To deallocate means to make the
file descriptor available for return by subsequent calls to \fIopen\fP()
or other functions
that allocate file descriptors. All outstanding record locks owned
by the process on the file associated with the file descriptor
shall be removed (that is, unlocked).
.LP
If \fIclose\fP() is interrupted by a signal that is to be caught,
it shall return -1 with \fIerrno\fP set to [EINTR] and the
state of \fIfildes\fP is unspecified. If an I/O error occurred while
reading from or writing to the file system during
\fIclose\fP(), it may return -1 with \fIerrno\fP set to [EIO]; if
this error is returned, the state of \fIfildes\fP is
unspecified.
.LP
When all file descriptors associated with a pipe or FIFO special file
are closed, any data remaining in the pipe or FIFO shall
be discarded.
.LP
When all file descriptors associated with an open file description
have been closed, the open file description shall be
freed.
.LP
If the link count of the file is 0, when all file descriptors associated
with the file are closed, the space occupied by the
file shall be freed and the file shall no longer be accessible.
.LP
If a STREAMS-based \fIfildes\fP is closed and the calling process
was previously registered to receive a SIGPOLL signal for events
associated with that STREAM, the calling process shall be unregistered
for events associated with the STREAM. The last
\fIclose\fP() for a STREAM shall cause the STREAM associated with
\fIfildes\fP to be dismantled. If O_NONBLOCK is not set and
there have been no signals posted for the STREAM, and if there is
data on the module's write queue, \fIclose\fP() shall wait for
an unspecified time (for each module and driver) for any output to
drain before dismantling the STREAM. The time delay can be
changed via an I_SETCLTIME \fIioctl\fP() request. If the O_NONBLOCK
flag is set, or if there
are any pending signals, \fIclose\fP() shall not wait for output to
drain, and shall dismantle the STREAM immediately.
.LP
If the implementation supports STREAMS-based pipes, and \fIfildes\fP
is associated with one end of a pipe, the last
\fIclose\fP() shall cause a hangup to occur on the other end of the
pipe. In addition, if the other end of the pipe has been named
by \fIfattach\fP(), then the last \fIclose\fP() shall force the named
end to be detached
by \fIfdetach\fP(). If the named end has no open file descriptors
associated with it and
gets detached, the STREAM associated with that end shall also be dismantled.
.LP
If \fIfildes\fP refers to the master side of a pseudo-terminal, and
this is the last close, a SIGHUP signal shall be sent to the
controlling process, if any, for which the slave side of the pseudo-terminal
is the controlling terminal. It is unspecified whether
closing the master side of the pseudo-terminal flushes all queued
input and output. 
.LP
If \fIfildes\fP refers to the slave side of a STREAMS-based pseudo-terminal,
a zero-length message may be sent to the master. 
.LP
When there is an outstanding cancelable asynchronous I/O operation
against \fIfildes\fP when \fIclose\fP() is called, that I/O
operation may be canceled. An I/O operation that is not canceled completes
as if the \fIclose\fP() operation had not yet occurred.
All operations that are not canceled shall complete as if the \fIclose\fP()
blocked until the operations completed. The
\fIclose\fP() operation itself need not block awaiting such I/O completion.
Whether any I/O operation is canceled, and which I/O
operation may be canceled upon \fIclose\fP(), is implementation-defined.
.LP
If a shared memory object or a memory mapped file remains referenced
at the last close (that is, a process has it mapped), then the
entire contents of the memory object shall persist until the memory
object becomes unreferenced. If this is the last close of a
shared memory object or a memory mapped file and the close results
in the memory object becoming unreferenced, and the memory
object has been unlinked, then the memory object shall be removed.
.LP
If \fIfildes\fP refers to a socket, \fIclose\fP() shall cause the
socket to be destroyed. If the socket is in connection-mode,
and the SO_LINGER option is set for the socket with non-zero linger
time, and the socket has untransmitted data, then
\fIclose\fP() shall block for up to the current linger interval until
all data is transmitted.
.SH RETURN VALUE
.LP
Upon successful completion, 0 shall be returned; otherwise, -1 shall
be returned and \fIerrno\fP set to indicate the error.
.SH ERRORS
.LP
The \fIclose\fP() function shall fail if:
.TP 7
.B EBADF
The \fIfildes\fP argument is not a valid file descriptor.
.TP 7
.B EINTR
The \fIclose\fP() function was interrupted by a signal.
.sp
.LP
The \fIclose\fP() function may fail if:
.TP 7
.B EIO
An I/O error occurred while reading from or writing to the file system.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.SS Reassigning a File Descriptor
.LP
The following example closes the file descriptor associated with standard
output for the current process, re-assigns standard
output to a new file descriptor, and closes the original file descriptor
to clean up. This example assumes that the file descriptor
0 (which is the descriptor for standard input) is not closed.
.sp
.RS
.nf

\fB#include <unistd.h>
\&...
int pfd;
\&...
close(1);
dup(pfd);
close(pfd);
\&...
\fP
.fi
.RE
.LP
Incidentally, this is exactly what could be achieved using:
.sp
.RS
.nf

\fBdup2(pfd, 1);
close(pfd);
\fP
.fi
.RE
.SS Closing a File Descriptor
.LP
In the following example, \fIclose\fP() is used to close a file descriptor
after an unsuccessful attempt is made to associate
that file descriptor with a stream.
.sp
.RS
.nf

\fB#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
.sp

#define LOCKFILE "/etc/ptmp"
\&...
int pfd;
FILE *fpfd;
\&...
if ((fpfd = fdopen (pfd, "w")) == NULL) {
    close(pfd);
    unlink(LOCKFILE);
    exit(1);
}
\&...
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
An application that had used the \fIstdio\fP routine \fIfopen\fP()
to open a file should
use the corresponding \fIfclose\fP() routine rather than \fIclose\fP().
Once a file is
closed, the file descriptor no longer exists, since the integer corresponding
to it no longer refers to a file.
.SH RATIONALE
.LP
The use of interruptible device close routines should be discouraged
to avoid problems with the implicit closes of file
descriptors by \fIexec\fP and \fIexit\fP(). This volume
of IEEE\ Std\ 1003.1-2001 only intends to permit such behavior by
specifying the [EINTR] error condition.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fISTREAMS\fP , \fIfattach\fP() , \fIfclose\fP() , \fIfdetach\fP()
, \fIfopen\fP() , \fIioctl\fP() , \fIopen\fP() , the Base Definitions
volume of
IEEE\ Std\ 1003.1-2001, \fI<unistd.h>\fP
.SH COPYRIGHT
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 .