Re: Text_IO from a stream

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Mon, 31 Mar 2008 21:17:10 +0200, Gautier wrote:

> Dmitry A. Kazakov:
>> But a stream has no defined formatting and is unrelated to ASCII.
> 
> Still, you can read the stream through Character'Read(s,c).

Yes, but will that be ASCII-encoded? And it has somehow invent lines and
pages.

>> Then the idea of parsing stream looks problematic. If you have in the stream a
>> sequence "  +  -", what Get should do after discovering '-'?
> 
> Exactly the same behaviour as when parsing an ill-formatted text.

Ah, yes. I cannot find the place in ARM, but it seems that Text_IO would
swallow syntactically incorrect input before propagating Data_Error.

> Reading a text file (or supposedly so) indirectly via a stream and Stream_IO 
> would have the same result that via Ada.Text_IO.
> 
>> Anyway, it is quite simple to do. You can do
>> 
>>    type Formatted_Stream (Source : access Root_Stream_Type'Class) is
>>       tagged limited private;
>>    function Get (Stream : access Formatted_Stream) return Integer;
>>    ...
>> 
>> The implementation of Formatted_Stream will use Source for all its I/O. So
>> you could hang it on any existing stream.
> 
> Fine, seems I need to rewrite a Text_IO for streams. I hoped for a ready-made 
> solution...

But Text_IO also defines all Get procedures on String. So if you knew where
line ends are in your stream you could cache the current line in
Formatted_Stream and then simply route all its Gets to Ada.Text_IO Gets.

> Well, I think I'll switch to a binary format...

I would do that too. Also I would override 'Read and 'Write in order to
make it platform-independent. (Stream_Element should be replaced by
octets.)

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de