Originální popis anglicky:
close - close a file descriptor
Návod, kniha: POSIX Programmer's Manual
#include <unistd.h>
int close(int
fildes);
The
close() function shall deallocate the file descriptor indicated by
fildes. To deallocate means to make the file descriptor available for
return by subsequent calls to
open() 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).
If
close() is interrupted by a signal that is to be caught, it shall
return -1 with
errno set to [EINTR] and the state of
fildes is
unspecified. If an I/O error occurred while reading from or writing to the
file system during
close(), it may return -1 with
errno set to
[EIO]; if this error is returned, the state of
fildes is unspecified.
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.
When all file descriptors associated with an open file description have been
closed, the open file description shall be freed.
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.
If a STREAMS-based
fildes 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
close() for a STREAM shall cause the STREAM
associated with
fildes 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,
close() 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
ioctl() request. If
the O_NONBLOCK flag is set, or if there are any pending signals,
close() shall not wait for output to drain, and shall dismantle the
STREAM immediately.
If the implementation supports STREAMS-based pipes, and
fildes is
associated with one end of a pipe, the last
close() 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
fattach(), then the last
close()
shall force the named end to be detached by
fdetach(). 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.
If
fildes 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.
If
fildes refers to the slave side of a STREAMS-based pseudo-terminal, a
zero-length message may be sent to the master.
When there is an outstanding cancelable asynchronous I/O operation against
fildes when
close() is called, that I/O operation may be
canceled. An I/O operation that is not canceled completes as if the
close() operation had not yet occurred. All operations that are not
canceled shall complete as if the
close() blocked until the operations
completed. The
close() 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
close(), is implementation-defined.
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.
If
fildes refers to a socket,
close() 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
close() shall block for up to the current linger interval
until all data is transmitted.
Upon successful completion, 0 shall be returned; otherwise, -1 shall be returned
and
errno set to indicate the error.
The
close() function shall fail if:
- EBADF
- The fildes argument is not a valid file
descriptor.
- EINTR
- The close() function was interrupted by a signal.
The
close() function may fail if:
- EIO
- An I/O error occurred while reading from or writing to the
file system.
The following sections are informative.
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.
#include <unistd.h>
...
int pfd;
...
close(1);
dup(pfd);
close(pfd);
...
Incidentally, this is exactly what could be achieved using:
dup2(pfd, 1);
close(pfd);
In the following example,
close() is used to close a file descriptor
after an unsuccessful attempt is made to associate that file descriptor with a
stream.
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#define LOCKFILE "/etc/ptmp"
...
int pfd;
FILE *fpfd;
...
if ((fpfd = fdopen (pfd, "w")) == NULL) {
close(pfd);
unlink(LOCKFILE);
exit(1);
}
...
An application that had used the
stdio routine
fopen() to open a
file should use the corresponding
fclose() routine rather than
close(). Once a file is closed, the file descriptor no longer exists,
since the integer corresponding to it no longer refers to a file.
The use of interruptible device close routines should be discouraged to avoid
problems with the implicit closes of file descriptors by
exec and
exit(). This volume of IEEE Std 1003.1-2001 only intends
to permit such behavior by specifying the [EINTR] error condition.
None.
STREAMS ,
fattach() ,
fclose() ,
fdetach() ,
fopen() ,
ioctl() ,
open() , the Base Definitions volume
of IEEE Std 1003.1-2001,
<unistd.h>
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
.
