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FREOPEN(3P)                POSIX Programmer's Manual               FREOPEN(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
       freopen - open a stream

SYNOPSIS
       #include <stdio.h>

       FILE *freopen(const char *restrict filename, const char *restrict mode,
              FILE *restrict stream);


DESCRIPTION
       The  freopen()  function  shall first attempt to flush the stream and close any file descriptor associated with
       stream. Failure to flush or close the file descriptor successfully shall be ignored. The error and  end-of-file
       indicators for the stream shall be cleared.

       The  freopen()  function  shall open the file whose pathname is the string pointed to by filename and associate
       the stream pointed to by stream with it. The mode argument shall be used just as in fopen().

       The original stream shall be closed regardless of whether the subsequent open succeeds.

       If filename is a null pointer, the freopen() function shall attempt to change the mode of the  stream  to  that
       specified  by mode, as if the name of the file currently associated with the stream had been used. It is imple-
       mentation-defined which changes of mode are permitted (if any), and under what circumstances.

       After a successful call to the freopen() function, the orientation of the stream shall be cleared,  the  encod-
       ing  rule shall be cleared,  and the associated mbstate_t object shall be set to describe an initial conversion
       state.

       The largest value that can be represented correctly in an object of type off_t shall be established as the off-
       set maximum in the open file description.

RETURN VALUE
       Upon  successful  completion,  freopen()  shall  return the value of stream. Otherwise, a null pointer shall be
       returned,  and errno shall be set to indicate the error.

ERRORS
       The freopen() function shall fail if:

       EACCES Search permission is denied on a component of the path prefix, or the file exists  and  the  permissions
              specified  by  mode are denied, or the file does not exist and write permission is denied for the parent
              directory of the file to be created.

       EINTR  A signal was caught during freopen().

       EISDIR The named file is a directory and mode requires write access.

       ELOOP  A loop exists in symbolic links encountered during resolution of the path argument.

       EMFILE {OPEN_MAX} file descriptors are currently open in the calling process.

       ENAMETOOLONG

              The length of the  filename  argument  exceeds  {PATH_MAX}  or  a  pathname  component  is  longer  than
              {NAME_MAX}.

       ENFILE The maximum allowable number of files is currently open in the system.

       ENOENT A component of filename does not name an existing file or filename is an empty string.

       ENOSPC The  directory  or  file  system  that  would contain the new file cannot be expanded, the file does not
              exist, and it was to be created.

       ENOTDIR
              A component of the path prefix is not a directory.

       ENXIO  The named file is a character special or block special file, and the device associated with this special
              file does not exist.

       EOVERFLOW
              The  named  file is a regular file and the size of the file cannot be represented correctly in an object
              of type off_t.

       EROFS  The named file resides on a read-only file system and mode requires write access.


       The freopen() function may fail if:

       EINVAL The value of the mode argument is not valid.

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.

       ENAMETOOLONG

              Pathname resolution of a symbolic link produced an intermediate result whose length exceeds  {PATH_MAX}.

       ENOMEM Insufficient storage space is available.

       ENXIO  A request was made of a nonexistent device, or the request was outside the capabilities of the device.

       ETXTBSY
              The file is a pure procedure (shared text) file that is being executed and mode requires write access.


       The following sections are informative.

EXAMPLES
   Directing Standard Output to a File
       The following example logs all standard output to the /tmp/logfile file.


              #include <stdio.h>
              ...
              FILE *fp;
              ...
              fp = freopen ("/tmp/logfile", "a+", stdout);
              ...

APPLICATION USAGE
       The  freopen()  function  is  typically used to attach the preopened streams associated with stdin, stdout, and
       stderr to other files.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       fclose(), fopen(), fdopen(), mbsinit(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdio.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
       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                          FREOPEN(3P)