Debugging Guidelines

Finding Bugs

To find bugs in your code, follow the steps below.

If you are getting a segmentation fault check your code using valgrind or gdb.
Make sure you are generating the expected results by using diff.
If your code generate the expected results in grace, but not in the submit server try valgrind. valgrind can help out identify the use of uninitialized variables and problems with dynamic memory allocation. It is extremely helpful.
Compile your code with gcc flags.
Run splint on your code. For example, splint my_prog.c.
If none of the above steps allows you to identify the problem try the following:
- Simplify the input/case that is generating the problem.
- Once you have simplify the input/case, use the debugger (gdb) to step through your code. Information on gdb basics can be found at gdb.

You get the correct results in grace, but not in the submit server - This may happen because:
- You have uninitialized variables. Grace seems to set uninitialized variables to 0.
- Your strings are missing a null character ('\0').
- You are not declaring an array that is large enough.
- You are passing to a function a pointer to a character rather than a pointer to an array of characters.
Your code might be generating a core dump in the submit server if for a test the submit server displays a message along the lines "expected ... but output ended".