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
                     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 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
                     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) 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)

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