Re: raised Constraint_Error?

[mfeldman@seas.gwu.edu (Michael Feldman)]

In article <Pine.SUN.3.91.950403111430.12054B-100000@babbage>,
Jeff Winchester  <winchest@csee.usf.edu> wrote:
>Could anyone tell me why the following code would cause a constraint 
>error?  I've been pulling out hairs for a couple of days now and am 
>obviously overlooking something simple.  Thanks.
>
Hmmm. I think it's going a bit far to ask net readers to
dig in so deep into your code. You need to do this sort of
detective work yourself, especially in a course. OTOH:

Some hints:

Your compiler ought to have a debugger, or at least give you a stack
dump when the Constraint_Error is propagated. This should tell you
in just which line the exception was raised, and where it propagated.

Constraint_Error in linked-list processing is most often caused by the
list-traversal loop walking right off the end of the list - a kind
of off-by-one problem.  When you reach the end of the list, and then
try to dereference a null pointer, Ada raises Constraint_Error.

If all else fails, add a Put_Line or two with a message that displays
each time you go around the loop.

Aren't they teaching debugging techniques at USF?

Mike Feldman
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Michael B. Feldman -  chair, SIGAda Education Working Group
Professor, Dept. of Electrical Engineering and Computer Science
The George Washington University -  Washington, DC 20052 USA
202-994-5919 (voice) - 202-994-0227 (fax) - mfeldman@seas.gwu.edu (Internet)
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