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CLOSE(3P)                  POSIX Programmer's Manual                 CLOSE(3P)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

NAME
       close - close a file descriptor

SYNOPSIS
       #include <unistd.h>

       int close(int fildes);


DESCRIPTION
       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 sig-
       nal  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 mod-
       ule'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  unref-
       erenced.  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  untransmit-
       ted data, then close() shall block for up to the current linger interval until all data is transmitted.

RETURN VALUE
       Upon  successful completion, 0 shall be returned; otherwise, -1 shall be returned and errno set to indicate the
       error.

ERRORS
       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.

EXAMPLES
   Reassigning a File Descriptor
       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);

   Closing a File Descriptor
       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);
              }
              ...

APPLICATION USAGE
       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.

RATIONALE
       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  behav-
       ior by specifying the [EINTR] error condition.

FUTURE DIRECTIONS
       None.

SEE ALSO
       STREAMS,   fattach(),   fclose(),   fdetach(),  fopen(),  ioctl(),  open(),  the  Base  Definitions  volume  of
       IEEE Std 1003.1-2001, <unistd.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, 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 .



IEEE/The Open Group                  2003                            CLOSE(3P)