Re: newbie problem

[Matthew Heaney <matthew_heaney@acm.org>]

Graeme Wallace <Dizzy@interact.net.au> writes:

> If I want to get user input for my program in the form of a  string of
> undefined length, how do I do so ?  If I set the string length to, say:
> 
> help_me_please : String(1..20);
> 
> I seem to be stuck with a string exactly that size.  What is the
> variable assignment which allows the actual length of the user input to
> determine the length of the string which the io system
> (ada.text_io.)gets ?

You have to allocate a buffer of some fixed size, as you have done.

What is missing from your solution is declaration of a "last" object,
whose value indicates the index value of the last valid character that
was input.

The standard idiom for doing this sort of thing is

declare
  Line : String (1 .. 80);
  Last : Natural;
begin
  Ada.Text_IO.Get_Line (Line, Last);

  ... Line (Line'First .. Last) ...

end;


The value of Last tells you how much of the buffer is actually in use.

Be careful not to name the Last object "Length."  That would be
misleading, and potentially error-prone, because "last index value" and
"length of input string" are two different concepts, and often have
different values.  They only have the same value here, because the first
index value of the string happens to be 1.