Exercises

Exercise 1: A segfault

Compile and run either segfault.c or segfault.cpp. It should cause a segfault.

  1. What tool would you use to find the problem?

  2. Identify the issue. What should the program actually do?

  3. Fix the program and test it.

Exercise 2: Divide by Zero (C++)

Try compiling and running divide_by_zero.cpp. This one throws an exception rather than just running along with incorrect results. That’s nice.

  • How would you go about finding the cause of the exception?

  • Use a debugger to inspect the code and look at the values passed to the function. What is the problem?

  • How would you fix the issue?

Exercise 3: The double pendulum (C)

This exercise is longer than the others and the code is more complex. If you brought your own code to debug, I suggest you look at that instead.

The code is at double_pendulum.c It runs a simulation of a double pendulum. It has some problems, though.

  1. Compilation errors

Try compiling the program with

$ cd examples
$ gcc -g -O2 double_pendulum.c -lm -o double_pendulum

The code does not compile. Can you find the problems following hints from the compiler or your IDE?

  1. Segfault

Once you manage to compile it, run the program with

$ ./double_pendulum

Now there’s a segmentation fault! Use a debugger to find where the segfault happens. Can you fix it?

Looks like it works! But does it, actually?

  1. Memory leak

You have received complaints from users. When the program runs for a long time, it takes a lot of memory. Maybe there is a memory leak.

Hint

You can separate valgrind output (and other errors) to a file using

$ valgrind --leak-check=full double_pendulum 2> valgrind_errors

  1. More?

Can you find another memory issue?

Hint

Use valgrind tool=memcheck and let the simulation run for a while.

Hint

What happens when a pendulum does not fit on the screen?