Re: raised CONSTRAINT_ERROR

[gisle@apal.ii.uib.no (Gisle S�lensminde)]

In article <86lmytp5i0.fsf@book.mteege.de>, Matthias Teege wrote:
>
>Moin,
>
>I made my first steps in Ada using GNATS under FreeBSD and
>now I have a problem that I didnt understand. The followig
>code gives me a raised CONSTRAINT_ERROR (in Line:
>StrArg := Ada.Command_Line.Argument(I)) and I didnt know
>why.

In the first version a string of length exactly 10 is used. In
the other version a generic string (allocated on stack) is
used. In Ada it's not allowed to assign strings of different
length, and the 

If you write on command line: 

% cldemo 0123456789 9876543210 abcdefghij 

The program will not give constraint error because all strings
is of the correct size. The string type have fixed size. If you 
want to handle dynamic sized strings use unbounded strings,
which is there to handle such cases. 

Another way is to use a block:

declare 
  Arg : String := Ada.Command_Line.Argument_Count;
begin
  put_line(Arg);
end;

This way a local variable arg (with desired size) is introduced.


>
>with Ada.Command_Line; use Ada.Command_Line;
>with GNAT.IO; use GNAT.IO;
>
>procedure Cldemo is
>
>Argcount: Natural;
>StrArg : String (1 .. 10);
>I: Positive := 1;
>
>begin
>   Argcount := Ada.Command_Line.Argument_Count;
>
>Schleife:
>   while I <= Argcount loop
>      StrArg := Ada.Command_Line.Argument(I);
>      Put_Line(StrArg);
>      I := I + 1;
>   end loop Schleife;
>
>end Cldemo;
>
>If I change the Code to
>
>with Ada.Command_Line; use Ada.Command_Line;
>with GNAT.IO; use GNAT.IO;
>
>procedure Cldemo is
>
>Argcount: Natural;
>I: Positive := 1;
>
>begin
>   Argcount := Ada.Command_Line.Argument_Count;
>
>Schleife:
>   while I <= Argcount loop
>      Put_Line(Ada.Command_Line.Argument(I));
>      I := I + 1;
>   end loop Schleife;
>
>end Cldemo;
>
>all works perfect. What is the main difference between
>both versions?
>
>Thanks for any hints
>Matthias
>


-- 
--
Gisle S�lensminde ( gisle@ii.uib.no )   

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