CS 102 Lab #9

This lab will give you practice with the debugger on our system, gdb. The file debug.C contains code that manipulates pointers, but there are several errors in the code. You must fix the code, and will use gdb to find out where the program is crashing and learn more about why.

The program uses a Node structure like the one in the last lab, and links together a short list of them. (It does not use any sort of list class -- it manipulates the pointers directly.) After building the list the code prints out its contents, then tests a function called Member that looks to see if a particular value is in the list.

Perform the following steps:

• Copy the files to your directory. (cp ~cs102/Lab9/* .)
• Compile the program with the -g flag. (g++ -g debug.C)
• Run the program to see what happens. (The program should die with a Segmentation fault.)
• Run your program within the debugger by doing the following:
  • Type gdb a.out to start the debugger
  • Type run at the gdb prompt to start the program running.
• Once the program stops, use the where command to see where the program died.
• Use the list command to see the lines of code immediately surrounding the fatal line.
• It's too late to see what happened just before the program stopped, so set a breakpoint inside the relevant function and type run again. (Type "help break" if you don't remember how to set breakpoints.)
• Once execution stops inside the function, use next to execute a line at a time until the program dies again. At each step, use print to display the value of relevant variables to see how they're changing.
• After watching the program die, you should understand what needs to be changed in the program to fix the error. Fix it and recompile with the -g flag.