Re: Get_Immediate has raised CONSTRAINT_ERROR : s-wchcnv.adb:207 explicit raise

[darek <darek.maksimiuk@gmail.com>]

So, are there any alternatives in Ada (GNAT) that should/may  be used for this trivial task? 

Regards,
  Darek 

On Wednesday, 18 February 2015 19:34:21 UTC+1, Dmitry A. Kazakov  wrote:
> On Wed, 18 Feb 2015 09:29:50 -0800 (PST), darek wrote:
> 
> > reading from a keyboard  keys such as arrow keys, PgUp, PgDn, etc. seems
> > to be a small challenge in Ada.  For this purpose one of the 
> > Get_Immediate procedures from the Ada.Text_IO shall be used.
> 
> shall?
> 
> > For the
> > keyboard we can use either 
> >   - procedure Get_Immediate  (Item : out Character) 
> >                or
> >   - procedure Get_Immediate  (Item : out Character; Available : out Boolean)
> > 
> > When I have used the Get_Immediate procedure with the extra  boolean
> > parameter, it  generates the constraint error for:
> >   - all arrow keys, PgUp, PgDn 
> >   - [ character from the keyboard !!!!
> > 
> > Is this a feature or a bug. How pressing a legal key can cause such a
> > weird result? 
> 
> Neither, I suppose.
> 
> AFAIK, RM does not mandate any specific mapping of non-character keyboard
> keys or, for that matter, any events from any possible input devices
> (mouse, joystick, pen, motion detector...) onto the type Character. Except
> for formatting keys (e.g. ones generating CR, LF, HT etc)
> 
> > The Get_Immediate procedure without the boolean parameter works fine but
> > it waits for a key to be pressed. 
> >
> > Any ideas how to avoid the problem with this exception? Am I missing something?
> 
> Yes. Page Up/Down are not a characters. No key necessarily is, however,
> some keys may have corresponding characters, or sequences of characters.
> 
> You shall not use Text_IO for keyboard input, unless under some ASCII
> terminal emulator, e.g. VT52 or VT100.
> 
> -- 
> Regards,
> Dmitry A. Kazakov
> http://www.dmitry-kazakov.de