CSE 333 Homework 0

Out: Wednesday, June 22, 2022
Due: Monday, June 27, 2022 by 11:59 pm.


The goal of Homework 0 is to make sure that all of the course infrastructure is working for you:

  1. You will fetch a source distribution that we have prepared.
  2. You will trivially modify a simple hello world C application, use make to compile it, and run it to learn the magic code.
  3. You will run tools to check the code for memory issues and potential style problems.
  4. You will package up and submit your code.

Homework 0 Instructions

Part A – Fetch the Code

Assignments will be distributed and collected using your CSE 333 GitLab repository. Starter code will be added to your repository by the course staff and you will tag your repository when you are done with an assignment to indicate which revision should be evaluated and graded by the course staff. More information about git and GitLab is given below and in other writeups on the course web site.

Clone your GitLab repository

You can use the CSE GitLab web interface to browse your files and find out information about your repository, but you must clone a copy to a Linux machine to do your work. If you have not done so already, change to a directory where you want to store the local repository for your CSE 333 projects, then follow the instructions on the Git Setup page to clone your CSE 333 repository. There is also additional information further down that page on Developing with Git.

You might have additional personal projects and repositories in GitLab for your own work, but be sure to use the repository provided by us for your CSE 333 course projects.

Once you have cloned the repository, change into that directory (it will be named something like cse333-22su-xyzzy, where xyzzy is your userid) then enter a ls command. You should see something like this:

bash$ git clone git@gitlab.cs.washington.edu:cse333-22su-students/cse333-22su-xyzzy.git
-- git output appears here
bash$ cd cse333-22su-xyzzy
bash$ ls -a
.gitignore clint.py exercises hw0
  • The .gitignore file lists file types that should not normally be saved in the repository. These are typically things like editor backup files (names ending in ~) and object files (ending in .o). They are files that are generated and used locally while you are working but are recreated as needed from files that are in the repository rather than archived permanently.
  • The exercises directory is mostly empty, but you can store your exercise code here. It is especially useful for collaborating with a partner and enabling course staff to access your code remotely (e.g., during virtual OH or when responding to your Ed post). It these cases, it would be best to push your current code to this folder for your partner or a staff member to view.

Part B – Edit, Compile, and Run hello_world

In the hw0 directory, run make. This command will use the instructions in file Makefile to compile the hello_world executable using the gcc compiler. Run the executable by entering the command ./hello_world. You should see one line of output that looks like:

bash$ ./hello_world
The magic code is: <xxxxx>

for some <xxxxx>. Now, edit hello_world.c in the CSE Linux environment using your favorite editor, and change the printf so that it instead says:

bash$ ./hello_world
The magic word is: <xxxxx>

Execute make to rebuild, and then re-run ./hello_world to make sure that it does what you expect.

Part C – Try GDB

You're unlikely to have any runtime errors, but let's use the debugger so that you know what it can do. Here is a session that:

  1. launches the debugger,
  2. sets a breakpoint on source line 19 of hello_world.c,
  3. prints the values of a couple of variables and an expression,
  4. prints a "backtrace" of the stack (showing the sequence of procedure calls that led to executing line 19 of hello_world.c), and then
  5. continues execution.

You should type the lines shown in italics. You may see some differences in version numbers or exact addresses, but the data values should be basically the same.

  • For GDB to be useful, you must use the -g option for gcc when compiling. The Makefile we distributed does that.
  • If you have already modified your file for Part B, you will see the new output word instead of "code" below.
bash$ gdb ./hello_world 
GNU gdb (GDB) Red Hat Enterprise Linux 8.3-1.el8
Copyright (C) 2019 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
Reading symbols ./hello_world...
(gdb) break 19
Breakpoint 1 at 0x401143: file hello_world.c, line 19.
(gdb) run
Starting program: /home/auser/cse333/hw0/hello_world

Breakpoint 1, main (argc=1, argv=0x7fffffffd668) at hello_world.c:19
19  printf("The magic code is: %X\n", a + b);
(gdb) print argv[0]
$1 = 0x7fffffffe394 "/home/auser/cse333/hw0/hello_world"
(gdb) print a
$2 = -889262067
(gdb) print /x a
$3 = 0xcafef00d
(gdb) print a+b
$4 = -559038737
(gdb) backtrace
#0  main (argc=1, argv=0x7fffffffd668) at hello_world.c:19
(gdb) continue
The magic code is: <xxxxxxxx>
[Inferior 1 (process 6760) exited normally]
(gdb) quit

Part D – Verify No Memory Issues

Throughout the quarter, we'll also be testing whether your code has any memory leaks or other memory errors (e.g., using uninitialized memory). We'll be using Valgrind to do this. Try out Valgrind for yourself so you know how to run it:

bash$ valgrind --leak-check=full ./hello_world

Note that Valgrind will print out that no memory issues were found.

Part E – Check for Style Issues

Another requirement during the quarter is that your code must follow the provided style guidelines. Although there are many opinions about what constitutes "good style," in this course, we will generally follow the Google C++ Style Guide for both C and C++ code. The repository files for this assignment included a Python script clint.py to check C source files for style issues. Try it yourself so you know how to run it:

bash$ ../clint.py hello_world.c

No style-checking tool is perfect, but you should try to clean up any problems that clint detects unless clint flags something that is definitely not a problem in this particular context (but be sure you have very good reasons to ignore any warnings).

Part F – Add a README.md File

Create a README.md file in directory hw0 that contains:

  • Your name
  • Your UW or CSE email address
  • A sentence that reveals the magic word you learned from Part B. Be sure that you actually say the magic word; do not just hint at what the word actually is.

We are not picky about the format of this file as long as it has all this information.

Homework Submission

Once you're done, "turning in" the assignment is done by creating an appropriate tag in your git repository to designate the revision (commit) that the course staff should examine for grading. But there are multiple ways to get this wrong, so you should carefully follow the following steps in this order. The basic idea is:

  1. Tidy up and be sure that everything is properly committed and pushed to your GitLab repository.
  2. Add a tag to your repository to specify the commit that corresponds to the finished assignment, after you have pushed all of your files.
  3. Check out a fresh copy of the repository in the CSE Linux environment and verify that everything works as expected.

Tidy Up and Commit

Commit all of your changes to your repository (see the beginning of the assignment or the main course web page for links to git information if you need a refresher on how to do this). Then in the hw0 directory:

bash$ git pull
bash$ make clean
bash$ git status
On branch master
Your branch is up-to-date with 'origin/master'.
nothing to commit, working directory clean

If you see any messages about uncommitted changes or any other indications that the latest version of your code has not been pushed to the GitLab repository, fix those problems and push any unsaved changes before going on. Then repeat the above steps to verify that all is well.

Tag Your Repository

Tag your repository and push the tag information to GitLab to indicate that the current commit is the version that you are submitting for grading:

bash$ git tag hw0-final
bash$ git push --tags

Do not do this until after you have pushed all parts of your homework solution to GitLab.

Check a Fresh Copy

To be sure that you really have updated everything properly, create a brand new, empty directory that is nowhere near your regular working directory, clone the repository into the new location, and verify that everything works as expected. It is really, really, REALLY important that this not be nested anywhere inside your regular, working repository directory.

bash$ cd <somewhere-completely-different>
bash$ git clone git@gitlab.cs.washington.edu:cse333-22su-students/cse333-22su-xyzzy.git
bash$ cd cse333-22su-xyzzy
bash$ git checkout hw0-final
bash$ ls
clint.py exercises hw0

Use your own userid instead of xyzzy, of course. The commands after git clone change to the newly cloned directory, then cause git to switch to the tagged commit you created in Step 2 above. We will do the same when we examine your files for grading.

At this point you should see your hw0 directory. cd into it, run make, run any tests you wish (something that will be crucial on future assignments). If there are any problems, immediately erase this newly-cloned copy of your repository (rm -rf cse333-22su-xyzzy), go back to your regular working repository, and fix whatever is wrong. It may be as simple as running a missed git push --tags command if the tag was not found in the repository. If it requires more substantive changes, you may need to do a little voodoo to get rid of the original hw0-final tag from your repository and re-tag after making your repairs.

To eliminate the hw0-final tag, do the following (this should not normally be necessary):

bash$ git tag -d hw0-final
bash$ git push origin :refs/tags/hw0-final 

Then make and commit and push your repairs, and only after all the changes are pushed, repeat the tag and tag push commands from Step 2. And then repeat this verification step to be sure that the updated version is actually correct.

Note: if you discover that repairs are needed when you check your work, it is crucial that you delete the newly-cloned copy and make the repairs back your regular working repository. If you modify files in the cloned copy you may wind up pushing changes to GitLab that will leave your repository in a strange state, and files may appear to mysteriously vanish. Please follow the instructions precisely.


For hw0, we'll give you full credit if you learn the magic code and correctly submit your work.