Debugging

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Debugging

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• Preventing bugs

• Detecting/locating bugs

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Thought Experiment

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• Everyone, form small groups of 3-4 people each.

• Discuss the following question:

  What are some things you can do to prevent bugs from occurring in your own programs?

• Goal: Come up with at least three or more different answers in your group.

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Bug Prevention

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• Design

• Good writing

• Self-checking code

• Test scaffolding

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Preventing Bugs Via Design

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• Good modularization / firewalls

• Strong encapsulation / information-hiding

• Clear, simple pre- and postconditions

• Requirements of operations should be testable

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Preventing Bugs Via Good Writing

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• Clarity of writing and style
  1. Use simple expressions, not complex
  2. Use meaningful names
  3. Clarity of purpose for:
     • Functions
     • Loops
     • Nested constructs
  4. Functions should only do a single thing

• Comments, comments, comments!!!!

• Small size of functions

• Use the smallest acceptable scope for:
  • Variable names
  • Static/local functions

• Use named intermediate values

• Use specifications (pre- and postconditions, invariants)

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Preventing Bugs Via Self-Checking Code

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• Assertions
  1. Checking assumptions
  2. "assert" macro
  3. Custom "assert" macros
  4. Assertions about intermediate values
  5. Loop invariants
  6. Module-level invariants

• Preconditions

• Postconditions

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Preventing Bugs Via Test Scaffolding

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• Test drivers

• Unit testing

• Integration testing

• Test suites

• Expected outputs

• Regression testing