Debugging Debugging CISC 323 Winter 2006 Prof. Lamb Prof. Kelly - - PowerPoint PPT Presentation

Debugging Debugging

CISC 323

Winter 2006

• Prof. Lamb
• Prof. Kelly

malamb@cs.queensu.ca kelly-d@rmc.ca

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Included in Courseware

• Required reading:

– “My Hairiest Bug War Stories”

• Marc Eisenstadt
• Communications of the ACM, April 1997
• Discussion

– What is debugging? – What three categories are identified by Eisenstadt to better understand debugging? – What experience have you had in debugging?

• Software? Hardware? Electronics? Mechanics? Anything else?

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What is Debugging?

• Various explanations

– The activity that is a consequence of successful testing – The process that results in the removal of the error – The process that locates and corrects the defect

» you hope!

• Wikipedia definition

– Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware thus making it behave as

• expected. Debugging tends to be harder when various

subsystems are tightly coupled, as changes in one may cause bugs to emerge in another.

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Human Aspects

• Quote on debugging by Schneiderman

– Debugging is one of the more frustrating parts of

• programming. It has elements of problem solving
• r brain teasers, coupled with the annoying

recognition that you have made a mistake. Heightened anxiety, and the unwillingness to accept the possibility of errors, increases the task

• difficulty. Fortunately, there is a great sigh of relief

and a lessening of tension when the bug is ultimately … corrected.

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High Level Approach to Debugging

1. Generate a hypothesis about the observed behaviour

• May involve doing some more testing

2. Test your hypothesis

– Obtain more data – Create new test cases – Trace code manually (inspect code) – Use interactive debugging tools

3. Hypothesis fails – go to 1. 4. Hypothesis passes

• Make changes to code
• Rerun tests
• that originally uncovered the bug
• that are affected by the code changes
• If any tests fail – go to 1

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Inspection vs. testing

• Considering debugging, what is the

advantage of code inspection over testing?

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Eisenstadt’s Categories

(fill in the details)

• Why bugs were difficult to track down
• Techniques used to track down the bugs
• Underlying causes of the reported bugs

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What experiences have you had debugging?

• Note: rerunning the compiler to get rid of

syntax errors is not debugging!

• Claim:

– Two of the biggest time wasters for non-software people trying to write and run software

• Not knowing how to test and debug
• Not knowing how to do version control