deferred class interface OUTPUT_STREAM
   --
   -- This abstract class is the superclass of all classes representing
   -- an output stream of bytes.
   --

feature(s) from OUTPUT_STREAM
   -- State of the stream:

   is_connected: BOOLEAN

feature(s) from OUTPUT_STREAM
   -- To write one character at a time:

   put_character (c: CHARACTER)
      require
         is_connected

feature(s) from OUTPUT_STREAM
   put_string (s: STRING)
      -- Output s to current output device.
      require
         is_connected;
         s /= Void

   put_unicode_string (unicode_string: UNICODE_STRING)
      -- Output the UTF-8 encoding of the unicode_string.
      require
         unicode_string /= Void

feature(s) from OUTPUT_STREAM
   -- To write a number:

   put_integer (i: INTEGER_64)
      -- Output i to current output device.
      require
         is_connected

   put_integer_format (i: INTEGER_64; s: INTEGER)
      -- Output i to current output device using at most s character.
      require
         is_connected

   put_real (r: REAL)
      -- Output r to current output device.
      require
         is_connected

   put_real_format (r: REAL; f: INTEGER)
      -- Output r with only f digit for the fractionnal part.
      -- Examples:
      --    put_real(3.519,2) print "3.51".
      require
         is_connected;
         f >= 0

   put_double (d: DOUBLE)
      -- Output d to current output device.
      require
         is_connected

   put_double_format (d: DOUBLE; f: INTEGER)
      -- Output d with only f digit for the fractionnal part.
      -- Examples:
      --    put_double(3.519,2) print "3.51".
      require
         is_connected;
         f >= 0

   put_number (number: NUMBER)
      -- Output the number.
      require
         number /= Void

feature(s) from OUTPUT_STREAM
   -- Other features:

   put_boolean (b: BOOLEAN)
      -- Output b to current output device according
      -- to the Eiffel format.
      require
         is_connected

   put_pointer (p: POINTER)
      -- Output a viewable version of p.
      require
         is_connected

   put_new_line
      -- Output a newline character.
      require
         is_connected

   put_spaces (nb: INTEGER)
      -- Output nb spaces character.
      require
         nb >= 0

   append_file (file_name: STRING)
      require
         is_connected;
         file_exists(file_name)

   flush
      -- forces a write of unwritten character (write my have been 
      -- delayed, flush writes buffered characters)



end of deferred OUTPUT_STREAM