Homework 3: Written Part

Learning about Makefiles

Hopefully you've done the lab activity on make. If not, please do that before continuing with this assignment.

Style Readings

In this assignment we will begin grading your code more strictly on style. Please read one (or both) of the following documents on style. (You can skip this part and save it for later, if you and your partner want to get right to coding.)

• Boswell and Foucher, The Art of Readable Code (2012)
• Martin, et al., Clean Code (2009)

The Questions

The written questions for this assignment can be completed individually or with your partner. Before you begin answering, decide whether you'll answer them together or you'll each do them separately. Either way, your answers are saved as you go, and you can come back and change them until the deadline.

Question 1 – Readings

Question 2 – Explaining Makefiles

Before answering this question, review the lab exercise on Makefiles and the help page on Working with Makefiles.

Question 3 – Reading Makefiles

If you haven't done so yet, clone the assignment repository on the CS 70 server so you can look at the code as you answer.

In the directory segfault-generator you'll find a simple program which uses one class (with a header) and one main file. In order to compile the generateSegfault executable, both .cpp files need to be compiled. The provided Makefile contains

• Two rules for compiling .cpp code into object files (i.e., machine instructions);
• One rule for linking these two object files into an executable program; and
• A helper rule so that we can say make clean to get back to the initial state with nothing compiled or linked.

Consider the following rule from the provided Makefile (which you are free to examine in more detail):

helloSayer.o: helloSayer.cpp helloSayer.hpp
    clang++ -c -o helloSayer.o -g -std=c++20 -pedantic -Wall -Wextra helloSayer.cpp

Question 4 – Running Makefiles

If you haven't already done so, cd to the segfault-generator directory and run the command

cs70-make generateSegfault

(cs70-make is a chattier version of make installed on the CS 70 server that explains what it is doing and why. If you're working somewhere else, plain make will do.)

Read over the output—you may need to make your terminal window bigger. See what actions cs70-make took and why.

Now that the program has compiled, run the command

touch generateSegfault.cpp

(The touch command sets the last-modified-time of a file to the current time, which will fool make into thinking we have made a change to the file, even though its contents are unchanged. The touch command is handy for testing/debugging Makefile rules, because you can easily check to see which commands make will run if a particular file appears to have changed.)

Now run the command again:

cs70-make generateSegfault

Read over the output and see what actions cs70-make took and why.

Question 5 – Improving Makefiles

The command make is the same as cs70-make but just less chatty. We'll switch to using it for the remaining examples.

If we just run make without specifying a specific target, then (only) the first target in the Makefile (and all its recursive dependencies) will be checked for possible rebuilding.

Question 6

Run make generateSegfault to generate the executable you can run. Then run the resulting executable (i.e., ./generateSegfault).

Choose a New Partner

Homeworks 4, 5, and 6 will be done with a new partner. You don't have to sort this out immediately, but start thinking about it now, and be sure to choose a partner and register before the deadline.

• Find your partner for Homeworks 4–6 on the pairing board

(When logged in, completion status appears here.)