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FOPEN(3)		     Library Functions Manual			FOPEN(3)

NAME
     fopen, fdopen, freopen -- stream open functions

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <stdio.h>

     FILE *
     fopen(const char * restrict path, const char * restrict 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
     letters:

     "r"     Open for reading.	The stream is positioned at the beginning of the
	     file.  Fail if the file does not exist.

     "w"     Open for writing.	The stream is positioned at the beginning of the
	     file.  Create the file if it does not exist.

     "a"     Open for writing.	The stream is positioned at the end of the file.
	     Subsequent  writes  to the file will always end up at the then cur-
	     rent end of file, irrespective of any intervening fseek(3) or simi-
	     lar.  Create the file if it does not exist.

     An optional "+" following "r", "w", or "a" opens the file for both  reading
     and writing.  An optional "x" following "w" or "w+" causes the fopen() call
     to fail if the file already exists.

     The mode string can also include the letter "b" after either the "+" or the
     first  letter.   This  is strictly for compatibility with ISO/IEC 9899:1990
     ("ISO C90") 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,  and
     do not require an intermediate seek as in previous versions of stdio.  This
     is  not portable to other systems, however; ANSI C requires that a file po-
     sitioning function intervene between output and input, unless an input  op-
     eration encounters end-of-file.

     The  fdopen()  function associates a stream with the existing file descrip-
     tor, fildes.  The mode of the stream must be compatible with  the	mode  of
     the  file	descriptor.  The "x" mode option is ignored.  When the stream is
     closed via fclose(3), fildes is closed also.

     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 origi-
     nal  stream (if it exists) is closed.  The mode argument is used just as in
     the fopen() function.

     If the path argument is NULL, freopen() attempts to re-open the file  asso-
     ciated  with  stream with a new mode.  The new mode must be compatible with
     the mode that the stream was originally opened with: Streams open for read-
     ing can only be re-opened for reading, streams open for writing can only be
     re-opened for writing, and streams open for reading and writing can be  re-
     opened in any mode.  The "x" mode option is not meaningful in this context.

     The  primary use of the freopen() function 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 argument 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), fileno(3), fseek(3), funopen(3)

STANDARDS
     The  fopen()  and	freopen()  functions  conform	to   ISO/IEC   9899:1990
     ("ISO  C90").   The  fdopen()  function  conforms	to  IEEE Std 1003.1-1988
     ("POSIX.1").

FreeBSD 9.1			October 17, 2011			FOPEN(3)
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