FOPEN(3S-SVR3)      RISC/os Reference Manual       FOPEN(3S-SVR3)



NAME
     fopen, freopen, fdopen - open a stream

SYNOPSIS
     #include <bsd/sys/types.h>

     #include <stdio.h>

     FILE *fopen (filename, type)
     char *filename, *type;

     FILE *freopen (filename, type, stream)
     char *filename, *type;
     FILE *stream;

     FILE *fdopen (fildes, type)
     int fildes;
     char *type;

DESCRIPTION
     fopen opens the file named by filename and associates a
     stream with it.  fopen returns a pointer to the FILE struc-
     ture associated with the stream.

     filename points to a character string that contains the name
     of the file to be opened.

     type is a character string having one of the following
     values:

          "r"  open for reading

          "w"  truncate or create for writing

          "a"  append; open for writing at end of file, or create
               for writing

          "r+" open for update (reading and writing)

          "w+" truncate or create for update

          "a+" append; open or create for update at end-of-file

     freopen substitutes the named file in place of the open
     stream.  The original stream is closed, regardless of
     whether the open ultimately succeeds.  freopen returns a
     pointer to the FILE structure associated with stream.

     freopen is typically used to attach the preopened streams
     associated with stdin, stdout and stderr to other files.





                        Printed 11/19/92                   Page 1

FOPEN(3S-SVR3)      RISC/os Reference Manual       FOPEN(3S-SVR3)



     fdopen associates a stream with a file descriptor.  File
     descriptors are obtained from open, dup, creat, or pipe(2),
     which open files but do not return pointers to a FILE struc-
     ture stream. Streams are necessary input for many of the
     Section 3S library routines.  The type of stream must agree
     with the mode of the open file.

     When a file is opened for update, both input and output may
     be done on the resulting stream.  However, output may not be
     directly followed by input without an intervening fseek or
     rewind, and input may not be directly followed by output
     without an intervening fseek, rewind, or an input operation
     which encounters end-of-file.

     When a file is opened for append (i.e., when type is "a" or
     "a+"), it is impossible to overwrite information already in
     the file.  fseek may be used to reposition the file pointer
     to any position in the file, but when output is written to
     the file, the current file pointer is disregarded.  All out-
     put is written at the end of the file and causes the file
     pointer to be repositioned at the end of the output.  If two
     separate processes open the same file for append, each pro-
     cess may write freely to the file without fear of destroying
     output being written by the other.  The output from the two
     processes will be intermixed in the file in the order in
     which it is written.

SEE ALSO
     creat(2), dup(2), open(2), pipe(2), fclose(3S), fseek(3S),
     stdio(3S).

DIAGNOSTICS
     fopen, fdopen, and freopen return a NULL pointer on failure.






















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