FOPEN(3)                       Library Routines                       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  follow‐
       ing 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 writing.  The file is created if it does not ex‐
                     ist.  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 characters in any of the two-
       character strings described above.  If the ``b'' is not specified, then
       the  file  is  assumed  to  contain  text.   On  input, carrige returns
       (``\r'') will be translated into  line  feeds  (``\n'').   The  reverse
       translation  will  occur on output.  If the ``b'' is specified, no such
       translation will occur.

       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)).

       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.  See the section on BUGS.

       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 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 in‐
                     valid.

       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) or stat(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).

BUGS

       If fdopen is passed a file descriptor in use by  another  stdio  stream
       (such as that available from the fileno macro), the result is currently
       undefined.  If you need to do such an operation, you should dup(2)  the
       result of the fileno macro before passing it to fdopen.

       Access bits are not currently checked for any file descriptor passed to
       fdopen which is a character-special file.

SEE ALSO

       open(2), stat(2), fclose(3), fseek(3), funopen(3)

STANDARDS

       The fopen and freopen functions conform to ANSI/C.  The fdopen function
       conforms to POSIX 1003.1 (1988).



GNO                              29 April 1997                        FOPEN(3)