Re: Should be getting a constraint error in this code

["Robert I. Eachus" <rieachus@comcast.net>]

Keith Boruff wrote:

> Hey all,
> 
> Forgive me for posting such a trivial problem here but I couldn't seem 
> to find an answer in any of the FAQs I know of nor DejaNews.
> 
> Though I'm not a novice programmer, I am a novice Ada programmer.

I suspect that the problem is that you are using GNAT, and forgot to 
read the fine manual.  If you expect integer overflow to be detected, 
you need to run gnatmake -gnato

The historical reasons for this are now ancient history.  The 
alternative is to use pragma Unsuppress.  If you insert it here:

> 
> In my studies this evening, I wrote the following trivial program to 
> force a constraint error:
> 
> with Ada.Text_Io; use Ada.Text_Io;
> 
> procedure Constraint_Tests is

pragma Unsuppress(Overflow_Check);
> 
>   type Exam_Mark is range 0 .. 100;
> 
>   English   : Exam_Mark := 72;
>   Math      : Exam_Mark := 68;
>   Computing : Exam_Mark := 76;
>   Average   : Exam_Mark;
> 
> begin
> 
>  Put("Average exam mark is ");
> 
>  -- I expect a constraint exception in this statement
>  -- because English + Math + Computing > 100
>  -- NOTE: On my machine, Exam_Mark'Base'Last = 127
>  Average := (English + Math + Computing) / 3;
>  Put_line(Exam_Mark'Image(Average));
> 
> end Constraint_Tests;
> 
> 
> Ok, the problem I'm having is that I'm expecting a constraint exception 
> to occur because (English + Math + Computing) = 216 and the largest 
> value of its base is 127 (on my machine).

Then you should get the result you expect.  I get:

F:\Ada\Test>constraint_tests
constraint_tests
Average exam mark is

raised CONSTRAINT_ERROR : constraint_tests.adb:21 overflow check failed

with either pragma Unsuppres, or -gnato, and 243 without.

-- 

                                           Robert I. Eachus

"The flames kindled on the Fourth of July, 1776, have spread over too 
much of the globe to be extinguished by the feeble engines of despotism; 
on the contrary, they will consume these engines and all who work them." 
-- Thomas Jefferson, 1821