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 differ (con-
       sult 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 implementation-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  encoding  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 offset 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, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                   FREOPEN(3P)