FOPEN(S)                 XENIX System V                  FOPEN(S)



     Name
          fopen, freopen, fdopen - Opens a stream.

     Syntax
          #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 be used to
          identify the stream in subsequent operations.

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

          r    Open for reading

          w    Create for writing

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

          r+   Open for update (reading and writing)

          w+   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.  It returns the original value of stream.  The
          original stream is closed, regardless of whether the open
          call ultimately succeeds.

          freopen is typically used to attach the preopened constant
          names stdin, stdout, and stderr to specified files.










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     FOPEN(S)                 XENIX System V                  FOPEN(S)



          fdopen associates a stream with a file descriptor obtained
          from open, dup, creat, or pipe(S).  The type of the stream
          must agree with the mode of the open file.  The type must be
          provided because the standard I/O library has no way to
          query the type of an open file descriptor.  fdopen returns
          the new stream.

          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 the end of the file.

          When a file is opened for append (that is, 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 output 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 process 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.

     See Also
          open(S), fclose(S)

     Diagnostics
          fopen and freopen return the pointer NULL if filename cannot
          be accessed.






















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