Re: need help learning Ada for a modula-2 programmer

[agent@drrob1.com]

On Sun, 02 Feb 2014 17:18:44 GMT, Brian Drummond
<brian3@shapes.demon.co.uk> wrote:

>On Sat, 01 Feb 2014 21:47:15 -0500, agent wrote:
>
>> On Tue, 28 Jan 2014 12:18:33 GMT, Brian Drummond
>> <brian3@shapes.demon.co.uk> wrote:
>> 
>> PROCEDURE GetCommandLine(CommandLine : OUT String) is BEGIN
>>   n := argument_count;
>>   k := 1;
>> 
>>   WHILE k <= n LOOP
>>     move(argument(k),argstr);   -  tried this-
>>     argstr := argument(k);         -- and this.  Neither works.
>> 
>>     cmdlinefrag := cmdlinefrag & argstr;
>>     cmdlinefrag := cmdlinefrag & ' ';
>>     k := Natural'SUCC(k);
>>   END LOOP; -- while k < n CommandLine := cmdlinefrag;
>> END GetCommandLine;
>
>> I am getting "wrong length for array of type string" errors.
>  
>Looking at this code I believe the immediate problem is a fixed length 
>"argstr" instead of a newly declared one (of the correct size!) for each 
>iteration of the loop. 
>
>But there's a wider problem in that the actual parameter for 
>CommandLine : OUT String needs to be correctly sized; or (as a function) 
>you need to build a correctly sized string piece by piece.
>
>Jeffrey has shown you a recursive way and there's (generally) nothing 
>wrong with that. (If your target system has 128 bytes of RAM, that's 
>another matter of course!).
>
>If you want a non-iterative approach, one way is to loop twice, first 
>calculating the required length, then declare the required length string 
>and loop again filling it. This string can then be returned as the 
>function result.
>
>function GetCommandLine return String is 
>   length : natural := 0;
>BEGIN
>   for i in 1 to argument_count loop
>      length := length + argument(i)'length;
>   end loop;
>   length := length + argument_count; -- for the spaces!
>   declare 
>      result : String (1 .. length);
>      pos : natural := 1;
>   begin
>      for i in 1 to argument_count loop
>         result(pos .. pos + argument(i)'length)
>            := argument(i) & " ";
>         pos := pos + argument(i)'length;         
>      end loop;
>      return result;
>   end;
>end GetCommandLine;
>
>> I was able to get this code working using variable length strings.  I
>> used bounded strings by copying the code from the texttools.common
>> routines.
>
>And finally there is nothing wrong with occasional use of bounded or 
>unbounded strings if you decide they are the best tool for the job (or if 
>it works and you don't want to mess with it further!) Don't infer that I 
>avoid them; they simply aren't usually my first choice!
>
>- Brian

No matter what I try, I'm getting a constraint error.  I don't
understand what's wrong.

The compiler noticed that FOR i in 1 to argument_count is wrong.
That's modula-2 syntax.

I missed that at first, even after the compiler complained.