Re: Newbie, returning strings in Ada

[Jeffrey Carter <jrcarter@acm.org>]

Santiago A. wrote:
> 2) This case works fine too:
> 
>         var U_Line:Unbounded_String;
>           ....
>         U_Line:=To_Unbounded_String(Get_Line(Sock));
> 
> 
> 3) This case fails 
> 
>         var F_Line:string:="1234567890";   
>          .....
>         F_Line:=Get_Line(Sock);

This is not Ada. Perhaps you are using Pascal; "var" is not part of 
Ada's syntax.

If you were using Ada, you might write

declare
    F_Line : String := "1234567890";
begin
    F_Line := Get_Line (Sock);
    ...
end;

The assignment to F_Line will usually raise Constraint_Error. The only 
time this will not raise an exception is when Get_Line returns a String 
of length 10, or if you have run-time checks suppressed. I suggest you 
not suppress run-time checking.

Using an Unbounded_String works because it's an abstraction that may 
hold a string of any length. An object of type String is always the same 
length.

> Is there any problem in a function that returns a string with lenght 2
> into a variable string(10)?

Yes.

> 
> Must the returned string and the variable that will hold the result be
> of the same length?

Yes. However, you can store the result in an object created for that 
purpose:

declare
    F_Line : [constant] String := Get_Line (Sock);
begin
    ...
end;

If you leave off "constant", then you can modify the value in F_Line. If 
you don't do that, though, it's best to mark the object as a constant.

-- 
Jeff Carter
"If I could find a sheriff who so offends the citizens of Rock
Ridge that his very appearance would drive them out of town ...
but where would I find such a man? Why am I asking you?"
Blazing Saddles