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 positioned at the beginning of the file.

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

       a+     Open for reading and appending (writing at end of file).	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 last character or as a character between the characters in any  of  the  two-
       character  strings  described above.  This is strictly for compatibility with ANSI X3.159-1989 (``ANSI C'') and has no effect; the ``b'' is
       ignored on all POSIX conforming systems, including Linux.  (Other systems may treat text files and binary files differently, and adding the
       ``b'' may be a good idea if you do I/O to a binary file and expect that your program may be ported to non-Unix environments.)

       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 positioning  function  inter-
       vene  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 necessary 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.

       Opening a file in append mode (a as the first character of mode) causes all subsequent write operations to this stream to occur at  end-of-
       file, as if preceded by an
	      fseek(stream,0,SEEK_END);
       call.

       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 compatible 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 indicators are cleared.  Modes "w" or "w+" do not cause truncation of the file.
       The file descriptor is not dup'ed, and will be closed when the stream created by fdopen is closed.  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
       function is to change the file associated with a standard text stream (stderr, stdin, or stdout).

RETURN VALUE

       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).

CONFORMING TO

       The fopen and freopen functions	conform  to  ANSI  X3.159-1989	(``ANSI  C'').	 The  fdopen  function	conforms  to  IEEE  Std1003.1-1988
       (``POSIX.1'').

SEE ALSO

       open(2), fclose(3), fileno(3)

BSD MANPAGE
							    2002-01-03								  FOPEN(3)