close

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
       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);


              #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(P)