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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 differ (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 unspeci-
       fied.  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 associ-
       ated 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 previ-
       ously registered to receive a SIGPOLL signal for events associated with
       that STREAM, the calling process shall be unregistered for events asso-
       ciated 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 unspeci-
       fied time (for each module and driver) for any output to  drain  before
       dismantling  the  STREAM.  The  time delay can be changed via an I_SET-
       CLTIME 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 asso-
       ciated 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 asso-
       ciated 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  can-
       celed.  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 con-
       tents 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.
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  stan-
       dard  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
       behavior 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, 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 .

IEEE/The Open Group                  2003                            CLOSE(3P)