Homework 3: Make Your Makefile

Now it's time to make your own Makefile! The Makefile will contain all the compilation and linking steps to make an executable called our-movie. You and your partner (together or individually) should complete the written questions in Part 1 before working on this part.

In the asciimation directory, you'll find quite a number of files. Specifically, you'll find:

• boundingbox.cpp and boundingbox.hpp: The implementation and header files for the BoundingBox class.
• boundingbox-test.cpp: A test program for the BoundingBox class.
• sprite.cpp and sprite.hpp: The implementation and header files for the Sprite class.
• sprite-test.cpp: A test program for the Sprite class.
• display.cpp and display.hpp: The implementation and header files for the Display class.
• display-test.cpp: A test program for the Display class.
• asciimation.cpp and asciimation.hpp: The implementation and header files for the Asciimation class.
• numsprites.hpp: A header file containing a constant indicating the number of sprites in the movie.
• our-movie.cpp: The main program that runs the movie.
• Makefile: A partially completed Makefile that you will finish.
• spriteImages/: A directory containing text files with ASCII art images for sprites.

Overall, there are four executables we can build (three test programs and the final movie program).

Reminder: Compiling by Hand

If we wanted to build each of the executables by hand, we would need to run the following commands to build boundingbox-test:

clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  boundingbox.cpp
clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  boundingbox-test.cpp
clang++ -o boundingbox-test boundingbox-test.o boundingbox.o -ltestinglogger

(You can try pasting the above commands into your terminal in the asciimation directory to see that they work and build the boundingbox-test executable.)

Similarly, we would run the following commands to build sprite-test (which will generate a slew of warning and error messages because the Sprite class isn't fully implemented yet):

clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  boundingbox.cpp
clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  sprite.cpp
clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  sprite-test.cpp
clang++ -o sprite-test sprite-test.o sprite.o boundingbox.o -ltestinglogger

We can build the display-test executable with:

clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  display.cpp
clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  display-test.cpp
clang++ -o display-test display-test.o display.o -lncurses

(Those commands will work, because the Display class is fully implemented.)

Finally, we can compile the our-movie executable with:

clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  boundingbox.cpp
clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  sprite.cpp
clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  display.cpp
clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  asciimation.cpp
clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  our-movie.cpp
clang++ -o our-movie our-movie.o asciimation.o display.o sprite.o boundingbox.o -lncurses

(These commands will also work, but the executable won't do much since many things are not yet implemented.)

For example:

• boundingbox.cpp uses boundingbox.hpp
• boundingbox-test.cpp uses boundingbox.hpp
• sprite.cpp uses sprite.hpp and boundingbox.hpp
• sprite-test.cpp uses sprite.hpp and boundingbox.hpp
• display.cpp uses display.hpp
• display-test.cpp uses display.hpp
• asciimation.cpp uses asciimation.hpp, display.hpp, sprite.hpp, boundingbox.hpp, and numsprites.hpp
• our-movie.cpp uses asciimation.hpp, display.hpp, sprite.hpp, boundingbox.hpp, and numsprites.hpp

and

• boundingbox-test needs to be relinked if boundingbox-test.o or boundingbox.o changes
• sprite-test needs to be relinked if sprite-test.o or sprite.o or boundingbox.o changes
• display-test needs to be relinked if display-test.o or display.o changes
• our-movie needs to be relinked if our-movie.o or asciimation.o or sprite.o or display.o or boundingbox.o changes

The make program reads a specification of what files depend on other files, and what commands to run to build each file. It then automatically determines what needs to be rebuilt based on which files have changed, and runs the appropriate commands to rebuild them.

The specification is written in a file called a “makefile” (but by convention, named Makefile with a capital 'M'). Once you've (correctly!) written a Makefile, you can simply type make in the terminal, and make will take care of everything for you.

An Initial Makefile

We've made a start on a nice Makefile for you in the asciimation directory. It contains some comments and a few example targets to get you started. (Specifically, it is able to build boundingbox-test and display-test, but it does not yet build sprite-test or our-movie.)

Your job is to fill in the rest of the Makefile so that it correctly builds all four executables, recompiling only what needs to be recompiled when you've made changes to one or more of the source or header files.

You can test it out by running one of the following commands in the terminal while in the asciimation directory:

• make clean to delete all the .o files and executables.
• make boundingbox-test to build the boundingbox-test executable.
• make display-test to build the display-test executable.
• make all makes both boundingbox-test and display-test.
• make builds the first target in the Makefile, which is all in this case.

The make program shows you the commands it runs, but it doesn't tell you why it's doing what it's doing. When you're debugging your Makefile, it can be handy to know what make is thinking. We've provided the cs70-make program, which does what make does, but also explains what it's doing and why. So if you're confused about why something isn't being rebuilt when you expected it to be, you can use cs70-make instead of plain make to get more insight.

For example, if we changed boundingbox.cpp and then ran make boundingbox-test, make would say something like the following, just listing the commands it ran:

clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  boundingbox-test.cpp
clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  boundingbox.cpp
clang++ -o boundingbox-test boundingbox-test.o boundingbox.o -ltestinglogger

But if we ran cs70-make boundingbox-test, we would get an explanation of why it decided to recompile each file:

- Making boundingbox-test
  - Found rule for boundingbox-test, prereqs: boundingbox-test.o boundingbox.o
  - Making boundingbox-test.o
    - Found rule for boundingbox-test.o, prereqs: boundingbox-test.cpp boundingbox.hpp
    - Making boundingbox-test.cpp
      + Okay, no rule found, but file exists
    - Making boundingbox.hpp
      + Okay, no rule found, but file exists
    + Target boundingbox-test.o doesn't need to be rebuilt (no newer prereqs)
  - Making boundingbox.o
    - Found rule for boundingbox.o, prereqs: boundingbox.cpp boundingbox.hpp
    - Making boundingbox.cpp
      + Okay, no rule found, but file exists
    - Making boundingbox.hpp (skipped, already made!)
    - Target boundingbox.o must be rebuilt because these prereqs are newer: boundingbox.cpp
    - Building: boundingbox.o
      - Running: clang++ -c -g -std=c++17 -pedantic -Wall -Wextra  boundingbox.cpp
    + Made boundingbox.o!
  - Target boundingbox-test must be rebuilt because these prereqs are newer: boundingbox.o
  - Building: boundingbox-test
    - Running: clang++ -o boundingbox-test boundingbox-test.o boundingbox.o -ltestinglogger
  + Made boundingbox-test!

Your Task: Finish Your Makefile and Use It

Read Over the Existing Makefile

Because we usually only make a Makefile once (tweaking it slightly as we add files to the project), people don't get a lot of practice writing them, and much of the time they'll start a new project by copying an existing Makefile and modifying it. For that reason, it's more important than ever to have a clear, nicely organized Makefile that is easy to read and understand and reminds people of all the little make details they might forget and uses all the little tricks that make it easy to maintain the file as the project grows.

Thus the provided Makefile uses two (optional) make features:

• Named variables to avoid repeating yourself. For example, the compiler and compiler flags are defined as variables at the top of the file, so if you want to change them, you only have to change them in one place.
• Automatic variables such as $@ and $< to avoid repeating yourself in the build commands.

The file contains comments explaining these features, so read through it carefully to understand how it works.

Finish the Makefile

There are three areas with TODO comments in the Makefile that you'll need to fill in to complete it. Specifically, you need to

• Add rules to build sprite.o and sprite-test.o, asciimation.o, and our-movie.o.
• Add rules to build sprite-test and our-movie.
• Add sprite-test and our-movie to them TARGETS variable, which will cause them to be listed both as prerequisites of the all target and to be deleted by the clean target.

Test Your Makefile

Once you've written your Makefile, you should be able to run cs70-make or make in the asciimation directory to generate any needed .o files, and to link the .o files to make the three executables: boundingbox-test, display-test, and our-movie. (Remember that building sprite-test will give you lots of warnings and errors, so you might not want to put it in TARGETS yet.)

clang++ -MM boundingbox.cpp

(When logged in, completion status appears here.)