Mehran Sahami Handout #33
CS 106A November 5, 2007
Debugging
Thanks to Eric Roberts and Nick Parlante for portions of this handout.
Much of your time as a computer programmer will likely be spent debugging. This
phenomena is best described by a quotation from one of the first computer pioneers,
Maurice Wilkes:
As soon as we started programming, we found to our surprise that it wasn’t as
easy to get programs right as we had thought. We had to discover debugging. I
can remember the exact instant when I realized that a large part of my life from
then on was going to be spent in finding mistakes in my own programs.
—Maurice Wilkes, 1949
In order to be better prepared to undertake the more complex future debugging that you
will be doing, we aim to give you here both a sense of the philosophy of debugging as
well as to teach you how to use some of the practical tips that make testing and debugging
easier.
The philosophy of debugging
Debugging is one of the most creative and intellectually challenging aspects of
programming. It can also be one of the most frustrating. To a large extent, the problems
that people face debugging programs are not so much technical as they are psychological.
To become successful debuggers, you must learn to think in a different way. There is no
cookbook approach to debugging, although Nick Parlante’s 11 Truths of Debugging
(given below) will probably help. What you need is insight, creativity, logic, and
determination. I've heard that Diet Coke™ helps too, but this may be anecdotal…
As computer scientists, it is important to remember that the programming process leads
you through a series of tasks and roles:
Task — Role
Design — Architect
Coding — Engineer
Testing — Vandal
Debugging — Detective
These roles require you to adopt distinct strategies and goals, and it is often difficult to
shift your perspective from one to another. Although debugging can often be very
difficult, it can be done. It will at times take all of the skill and creativity at your disposal,
but you can succeed if you are methodical and don’t give up on the task.
Debugging is an important skill that you will use every day if you continue in Computer
Science or any related field. Even though it is the final task of those listed above, it is
certainly not the least important. You should always plan ahead and allow sufficient time
for testing and debugging, as it is required if you expect to produce quality software. In
addition, you should make a concentrated effort to develop these skills now, as they will
be even more important as programs become more complicated later in the quarter.
