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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: GNAT.Serial_Communication and Streams
Date: Sun, 22 Nov 2015 21:52:02 +0000
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Date: 2015-11-22T21:52:02+00:00
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rrr.eee.27@gmail.com writes:

> I want to send text strings via a serial line (actually, it is a USB
> device that presents itself as a serial CDC device).
>
> For sending text snippets I had to declare the following routine:
>
>    procedure Send_Command (Cmd : String)
>    is
>       Output_Max_Length : constant Ada.Streams.Stream_Element_Offset := 50;
>       Output : Ada.Streams.Stream_Element_Array (1 .. Output_Max_Length);
>    begin
>       for I in 1 .. Cmd'Length loop
>          Output (Ada.Streams.Stream_Element_Offset(I)) := Character'Pos(Cmd (Cmd'First + I - 1));
>       end loop;
>       Output (Cmd'Length+1) := Character'Pos(ASCII.LF);
>       GNAT.Serial_Communication.Write (P, Output(1..Cmd'Length+1));
>    end Send_Command;
>
>
> That works but feels completely strange to me. I'm sure that I'm
> missing something here. There must be an easier way to fill the output
> buffer with a standard string.

The clue is that

   type Serial_Port is new Ada.Streams.Root_Stream_Type with private;

which means that you aren't supposed to use the local Read/Write; they
are for the implementation of the 'Read/'Write type attributes (ARM
13.3.2),

   String'Write (P'Access, Cmd & ASCII.LF);

BTW, you should probably have declared

   Output : Ada.Streams.Stream_Element_Array (1 .. Cmd'Length + 1);

avoiding the need for Output_Max_Length.