Lecture 11 – Feb 26th, 2020


  1. Log in to clyde.
  2. Create a directory and cd into it.
  3. Copy ~steve/ex/mc_pi.c, ~steve/ex/logger.h, ~steve/ex/logger.c, ~steve/ex/rand.h and ~steve/ex/rand.c into the directory.


  1. Based on the example Makefile in the slides, create a Makefile to compile the program mc_pi. Make sure you look through each .c file to see which .h files it includes so you can set up the prerequisites correctly.

    If you have put -std=c11 in the CFLAGS variable (and you should), you’ll get an error and a warning like this.

    mc_pi.c:49:18: warning: implicit declaration of function 'getopt' is invalid in C99 [-Wimplicit-function-declaration]
      while ((flag = getopt(argc, argv, "hn:v")) != -1) {
    mc_pi.c:52:21: error: use of undeclared identifier 'optarg'
          trials = atoi(optarg);
    1 warning and 1 error generated.

    To fix that, add -D_POSIX_C_SOURCE=200809L to CFLAGS.

    When you run $ make, it should build three object files (those ending in .o) and the program mc_pi.

  2. Run $ ./mc_pi a few times to see what it does. Run $ ./mc_pi -h to get the help. Run mc_pi again but change the number of trials. Try small values and large values. Try nonsensical values (or no value at all).
  3. The touch command can be used to change the time stamp on a file without changing any of its contents. We can use this to test the Makefile.

    First, run $ make again. If you haven’t changed any files, make should say it has nothing to do. Next, run $ touch logger.c and then rerun make. If everything worked correctly with your Makefile, logger.o and mc_pi should be remade but nothing else.

  4. Run touch on rand.h and rerun make. Did it rebuild the right files?
  5. If you didn’t do so in step 1, add phony all and clean targets. all should depend on mc_pi and have no recipe. clean shouldn’t depend on anything but should remove mc_pi and the object files. Make sure you don’t delete your source files!

    Remember, all should be the first target in the Makefile. Running $ make and $ make all should have the same effect. Test that $ make clean performs the correct action.

    Recall that to make a phony target, you add it as a prerequisite to the .PHONY so you should have the line

    .PHONY: all clean
  6. Remove clean from the .PHONY: all clean line of the Makefile. Run $ touch clean. This will create an empty file named clean. Run $ make clean and note what happens.
  7. Readd clean to .PHONY: and run $ make clean again. It should perform the clean action even though the clean file is present. Remove the clean file.
  8. Add logging to rand.c to log (with LOG_LEVEL_INFO) each random value that is produced. log_message takes a variable number of arguments where the first one is the log level, the second is a printf-style format string, and the remaining are the arguments to print according to the format string’s conversion specifiers. You can use %f to print out the double.

    Make sure you include the appropriate header and update the dependencies in your Makefile.

  9. Run mc_pi with the -v argument. You might want to have just a few trials to avoid spamming your terminal with a few hundred random values. You can also redirect the messages to a file using $ ./mc_pi -v -n 1000 2>generated_files.