The Daily Cow

I can't claim to be familiar with Makefiles, but after these mishaps I can confidently assert that I've learned a thing or two about them.

The first error was easy to catch and fix: Tabs and spaces are completely different! For each label, the dependencies list must come after a space, not a tab; but the instructions must be tab-prefixed.

The second error took hours (and the help of my CS professor) to figure out: Makefiles should NOT contain the \r (linefeeds) that are inserted by Windows text editors but are invisible in almost all text editors in their default settings. I could not make anything of the inscrutable error I got each time: 'ake: Fatal error: Don't know how to make target `main.o Why? Because the Makefile itself looked just fine! I've made Makefiles before, and that's what they all looked like. It wasn't until my professor opened up my Makefile in vi did he see that it had those Windows characters that *nix systems dislike. Whoops. There goes three hours.

The third problem I did not even detect until I heard that I failed every automated test on my program. I was appalled by that! I was absolutely certain my code was functional and worked correctly. It turns out, I must insert a @ in front of my instructions in order to suppress Make's output to stdout. When my output was compared to the correct output, it was off by the output from Make. Whoops.

So if you ever need to deal with Makefiles, just make sure you keep these things in mind. Otherwise, Makefiles are intuitively pretty simple.

I get asked about programming mishaps--bugs I've encountered, obstacles I had to cross, etc--in my interviews, and I can never come up with anything, leading them to think of me as a snotty little kid who thinks he's too good to make mistakes. Well, I just don't remember them specifically, so I thought it might be helpful if I kept a repository of programming mishaps I encounter on the Daily Cow. Writing will make me remember them, right?

I have one right now, which I'll write up soon. For an example of what I mean, check out my previous post about a CS project in which not realizing that I needed a terminating newline led my program to produce inscrutable errors.

Three things, one directly my fault and the other two not, caused me to waste eight otherwise-productive hours on the second project. You'll see how ridiculous those three things are.

I thought I had a completely functional submission yesterday morning. All I needed to do was to use the test script once to verify that. But when I uploaded it, the test script wouldn't even run. After some time of research (my professor was out of town and nobody else had the same problems), I discovered that it was because I was running Bash as my default shell. I changed that to csh (C-shell) and now the script finally ran.

I failed every test. It gave me absolutely useless explanations for why I failed them, but I found one lethal error that could have caused me to fail them all: instead of using sb $0, 0($a0) to save a null character, I used lb $0, 0($a0) (which obviously doesn't work). After I fixed that (using notepad), I uploaded the file again, and it still failed all the tests. I read through the code again, but I found no bugs!

I opened Mars (our MIPS assembler) and tried running the code, and surprisingly it worked, so I saved it (even though I made no changes) and uploaded it. And now the tests don't complain that they failed--instead they complain about some command not being found. After Googling a bit, I realized that that command isn't in csh, but it's in tcsh. So I changed my shell to that, and program passed all tests--yay!

Now that I was confident my code worked, I put off the last part--commenting the code (yup, the whole assembly file was nearly uncommented when I wrote it) until 10:40. But after commenting, the code stopped working--it failed all the tests again! I was so confused! So I replaced code bit by bit to see what made it work, and only at 11:55 did I figure out that this whole time, the only reason the test script failed me completely was that I didn't have a newline at the very end of my program.

And this is also why opening and saving in Mars, even with no changes, fixed my program up above (paragraph 2). Isn't that stupid? How should I have known that I shouldn't use Notepad to edit my program? (it doesn't automatically add a newline) How should I have known that the script works only on tcsh? I suppose it was unwise of me to change my settings away from the default, but isn't that what settings are for?

Part of it was lack of documentation on Clancy (my professor)'s part--a simple "The script only works on tcsh and on newline-terminated code" would have sufficed to save me 4 hours! The other part was a bona fide mistake of a programmer. (I made one typo!) But together they were disaster because nobody else had the same problems. Lesson: There are dangers to doing things unconventionally.