Re: Out_File , excess line

[Simon Wright <simon@pushface.org>]

comicfanzine@gmail.com writes:

> But , when we try to open the file manually , the text editor print :
>
> " This is not a text file . Type unknown . "
>    PACKAGE ST_IO RENAMES Ada.Streams.Stream_IO ;
>
>    test_file : ST_IO.File_type ;
>
>    Input_Stream : ST_IO.Stream_Access ;
[...]
>    ST_IO.Create( File => test_file ,
>                Mode => ST_IO.Out_File ,
>                Name => "test" );
>
>     Input_Stream := ST_IO.Stream( test_file );
>
>     for j in 1..case_array'Length loop
>       Unbounded_String'Write( Input_Stream , case_array(j) );
>    end loop;

'Input_Stream' is a very odd name for a stream you're going to *output*
to.

What's happening is that (reasonably, though not as far as I can see
discussed by the standard) GNAT treats Unbounded_String'Write as if an
unbounded string is a discriminated type whose discriminants have
defaults; that is, the discriminants (the array bounds) are output to
the stream first, followed by the characters of the string. (This is
what happens for String'Output; String'Write doesn't include the bounds;
is the Unbounded_String'Write behaviour a bug or a feature?).

So, if you Unbounded_String'Write "foo", you will get
- 4 bytes containing binary 1, the first index of the content
- 4 bytes containing binary 3, the last index of the content
- 3 bytes of content, 'f' 'o' 'o'.

Which looks nothing like a text file.

You could try

  String'Write (Input_Stream, To_String (case_array (j)) & ASCII.LF);

(should be OK on Unix systems, don't know about Windows. A text
editor should be OK with LF-terminated lines, Notepad not so much.)

[1] http://www.ada-auth.org/standards/12rm/html/RM-13-13-2.html#p9.1