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


NAME
       fopen, fdopen, freopen - stream open functions

SYNOPSIS
       #include <stdio.h>

       FILE *fopen( char *path, char *mode);
       FILE *fdopen( int fildes, char *mode);
       FILE *freopen( char *path, 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.
       Linux may not behave this way.

       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, and do not require an intermediate seek as



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


       in previous versions of stdio.  This is  not  portable  to
       other  systems,  however,  and  may  not  work under Linux
       (someone should find out and fix  this  manpage);  ANSI  C
       requires   that  a  file  positioning  function  intervene
       between  output  and  input,  unless  an  input  operation
       encounters end-of-file.

       The  fdopen function associates a stream with the existing
       file descriptor, fildes.  The mode of the stream  must  be
       compatible with the mode of the file descriptor.

       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, fclose,

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








BSD MANPAGE              29 November 1993                       2