Comment by caf
10 years ago
But that's not what this study is about: everyone agrees that stomping wildly off the end of an array in C is not going to end well.
This is about far more subtle issues than that - issues where there is some disagreement about whether it's OK to do or not. And the GP is right - these are often not such a problem in practice, if only because these are the kinds of issues where experienced C programmers know that they're sailing close to the wind, and there's almost always an alternative construct that's on more solid ground.
Signed versus unsigned comparison, signed wrap-around, undefined division behaviour, undefined behaviour of some casts, and strict aliasing optimisations have all caused hard bugs that I've had to spend a lot of time fixing.
I had to deal with some of these before I was a compiler writer, and I would end up just kind of kicking my code repeatedly until stuff worked again.
Now that I'm a compiler writer, I know how to recognize what is happening, but I'm still not smart enough to avoid the bugs in general and I still spend time fixing bugs that result from these issues.
So, I'm with pcwalton: it is a problem. Maybe I don't see it every day, but I see it probably at least once a month.
There are fewer issues that scare me more than undefined behavior that usually works. "Works" enough for programmers to add it, knowingly or unknowingly, even to defend it as "working in practice"... only to leave a needle in a haystack that they'll never find.