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Four more anti-patterns

Another set of absolutely lovely gems we found this week: an empty for, the almost-impossible if, continue just because, and source that doesn’t match the executable. Oh my!

The empty for

I’d seen this before, but we found it again while trying to diagnose an (unrelated) infinite loop bug in our source (more on that below):

for (;;) {
   // lots of things
   if (someCondition) {

Not sure why a while loop wouldn’t have sufficed… Wait, it does—that’s what I replaced it with! My solution looked roughly like this:

bool doneSearching = false;
while (!doneSearching) {
   // lots of things
   if (someCondition) {
      doneSearching = true;

Of course, as usual, that’s a good deal less obscure and contrived than the original. (The first time I saw the original, my eyes about bugged out. It’s not something I’d ever considered doing, especially since there is no reason to ever do it that way.)

The almost-impossible if

In the same section of code, we discovered this fun guy:

if (h < 0.1 * h)
   h *= 0.1

I have no idea what that is supposed to accomplish; the only time it would ever work is if h is negative—and you couldn’t pick a less clear way to pull that off without some serious effort. But since we have no idea what the code is trying to do—there are no comments, and it’s implementing an undocumented and unremembered algorithm—we’ve left it as is.

Say continue just because

Another module in the same program has the following program flow:

int i;
for (i = 0; i < someNum; i++) {
   // bunches of things
   if (someCondition) {
      // a few things
   } else {
      // a few other things

That’s it. For some reason, the previous developer decided he needed to make sure the for loop continued executing immediately after the if statement finished. Of course, it does that anyway. Perhaps it was left after other code that used to follow the conditional block was (re)moved; who knows? In any case, it made for an amusing example.

Working executable, broken source

The single most frustrating “anti-pattern” we ran into this week was finding two separate executables that clearly work differently than our current source does. This probably sounds crazy, and it may not even make sense, so allow me to elaborate.

In the first case we found, there is a version of the program used in house that works basically as expected. As with any piece of production software, it has some bugs, but for the most part it runs normally and gives the desired results. When we built it again this week in preparation for making some changes, we discovered to our horror that it gets caught in an infinite loop. Given that the version used internally works as expected, this was a shock, to say the least. Apparently, at some point someone started changing the program but never finished. Fixing it will be… fun.

The second example is a launcher program that spools off a set of other related executables in order to accomplish various tasks. Beyond the first-order frustration that it can only be build in Visual Studio 6.0 (from June 1998, and yes that is almost 15 years ago), the list of programs to spool off is out of date and inaccurate. We don’t know how this came to be, either.

In both cases, we’ll get past it; we have the know-how, and while it might be painful, we can gather enough information to fix things. But it hammers home again the value of writing code carefully and maintainably.

Or, as a friend of mine put it recently:

Always code as if the person who ends up maintaining your code is a violent psychopath who knows where you live.