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

[agent@drrob1.com]

On Sun, 02 Feb 2014 19:10:16 -0500, agent@drrob1.com wrote:

>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.
>
>

I just figured out the constraint error.  I was using a simple
assignment.  When I started using the move command, it started
working.

I just needed to make the statement
  pos := pos + argument(i)'length + 1;  

Now it works.

Every human language has its idioms, and computer languages are not an
exception.

Thanks guys