Lecture Notes for Advanced Programming II

15 February 2001 - Debugging

1. debugging

   1. some technology, some psychology

   2. technology - unchecked array access; explicit dynamic storage management; complex rules

   3. psychology - hard to see your mistakes; hard to face your mistakes

   4. terminology - there's the cause, then there's the symptoms

2. understand the symptoms

   1. make sure it's a problem - proper behavior, fast execution

   2. make sure you know what the problem is - sometimes it's obvious, sometimes it isn't

3. look for clues

   1. what data causes the symptoms

   2. what was changed last - use source code revision; sccs, rcs, cvs

4. create your own clues

   1. use assert statements to check arguments and results

      1. #include <cassert>
         void set(unsigned x)
           assert(x < x_extent);
         

      2. can also use #include <assert.h>

   2. program defensively

      1. if (line.is_horizontal()) // blah blah blah
         else if (line.is_vertical()) // blah blah blah
         else { cerr << "line isn't horizontal or vertical\n" ; abort() }
         

      2. always have a default switch branch

   3. use debugging print statements

5. finding the cause

   1. know your mistakes

6. debuggers and other tools

   1. know how to use the debugger - just the basics; stack trace, stop, print

   2. enable everything on the compiler - ansi standards, extra checks and warnings, debugging code

   3. use other tools - lint, purify, malloc debug libraries, other languages

This page last modified on 27 February 2001.