FOPEN(3)            Linux Programmer's Manual            FOPEN(3)

NAME
       fopen, fdopen, freopen - stream open functions

SYNOPSIS
       #include <stdio.h>

       FILE *fopen (const char *path, const char *mode);
       FILE *fdopen (int fildes, const char *mode);
       FILE  *freopen  (const  char *path, const char *mode, FILE
       *stream);

DESCRIPTION
       The fopen function opens the file whose name is the string
       pointed to by path and associates a stream with it.

       The argument mode points to a string beginning with one of
       the following sequences (Additional characters may  follow
       these sequences.):

       r      Open  text  file  for reading.  The stream is posi-
              tioned at the beginning of the file.

       r+     Open for reading and writing.  The stream is  posi-
              tioned at the beginning of the file.

       w      Truncate  file  to  zero length or create text file
              for writing.   The  stream  is  positioned  at  the
              beginning of the file.

       w+     Open  for reading and writing.  The file is created
              if it does not exist, otherwise  it  is  truncated.
              The  stream  is  positioned at the beginning of the
              file.

       a      Open for writing.  The file is created if  it  does
              not  exist.  The stream is positioned at the end of
              the file.

       a+     Open for reading and writing.  The file is  created
              if  it does not exist.  The stream is positioned at
              the end of the file.

       The mode string can also include the letter  ``b''  either
       as a third character or as a character between the charac-
       ters in any of the two-character strings described  above.
       This  is  strictly for compatibility with ANSI C3.159-1989
       (``ANSI C'') and has no effect; the ``b'' is ignored.

       Any      created      files      will      have       mode
       S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP|S_IROTH|S_IWOTH (0666), as
       modified by the process' umask value (see umask(2).

       Reads and writes may be intermixed on  read/write  streams
       in any order.  Note that ANSI C requires that a file posi-
       tioning  function  intervene  between  output  and  input,
       unless  an  input  operation  encounters end-of-file.  (If
       this condition is not met,  then  a  read  is  allowed  to
       return  the  result of writes other than the most recent.)
       Therefore it is good practice (and indeed sometimes neces-
       sary  under  Linux)  to  put an fseek or fgetpos operation
       between write and read operations on such a stream.   This
       operation  may  be an apparent no-op (as in fseek(..., 0L,
       SEEK_CUR) called for its synchronizing side effect.

       The fdopen function associates a stream with the  existing
       file  descriptor,  fildes.  The mode of the stream (one of
       the values "r", "r+", "w", "w+", "a", "a+") must  be  com-
       patible  with  the  mode of the file descriptor.  The file
       position indicator of  the  new  stream  is  set  to  that
       belonging to fildes, and the error and end-of-file indica-
       tors are cleared.  Modes "w" or "w+" do not cause  trunca-
       tion of the file.  The file descriptor is not dup'ed.  The
       result of applying fdopen to a  shared  memory  object  is
       undefined.

       The  freopen  function  opens  the  file whose name is the
       string pointed  to  by  path  and  associates  the  stream
       pointed  to by stream with it.  The original stream (if it
       exists) is closed.  The mode argument is used just  as  in
       the  fopen function.  The primary use of the freopen func-
       tion is to change the file associated with a standard text
       stream (stderr, stdin, or stdout).

RETURN VALUES
       Upon  successful  completion  fopen,  fdopen  and  freopen
       return a FILE pointer.  Otherwise, NULL  is  returned  and
       the global variable errno is set to indicate the error.

ERRORS
       EINVAL The  mode provided to fopen, fdopen, or freopen was
              invalid.

       The fopen, fdopen and freopen functions may also fail  and
       set  errno for any of the errors specified for the routine
       malloc(3).

       The fopen function may also fail and set errno for any  of
       the errors specified for the routine open(2).

       The fdopen function may also fail and set errno for any of
       the errors specified for the routine fcntl(2).

       The freopen function may also fail and set errno  for  any
       of   the   errors  specified  for  the  routines  open(2),
       fclose(3) and fflush(3).

SEE ALSO
       open(2), fclose(3)

STANDARDS
       The  fopen  and  freopen   functions   conform   to   ANSI
       C3.159-1989 (``ANSI C'').  The fdopen function conforms to
       IEEE Std1003.1-1988 (``POSIX.1'').

BSD MANPAGE              13 December 1995                       1