Is that a compiler bug?

by bbatsell on 2/14/2010, 9:57 PM with 8 comments
  • by dadkins on 2/15/2010, 3:30 AM

    I was skeptical about his example of a compiler bug. Take the following similar example:

        int bar(void) {
        unsigned x = 1;
        int y = -1;
        return x > y;
    }
    Surprisingly, the result is always 0, at least on every version of gcc I've tried. How could this be? It turns out unsigned's are one area where the C standard really screwed up. When comparing a signed and an unsigned value, the compiler helpfully promotes the signed (-1) to unsigned.

    I was surprised the given example with chars instead of ints didn't give the same result. Was it really a bug, or just ambiguity in the standard?

  • by patio11 on 2/15/2010, 1:24 AM

    Compiler bugs are like lupus. It's not lupus, either.

    Relatedly, a certain outsourcing company I can't name really, really needs to stop closing every ticket with "We investigated and it should work fine, so it is probably a framework bug." Particularly when the code at issue looks like:

    String someLabel = null; someLabel.split(","); // throws NPE. Probably framework bug.

  • by yread on 2/15/2010, 12:16 AM

    Why doesn't gcc emit warning Wsign-compare for the first example? Why does it emit it only for C++ code?

  • by Groxx on 2/14/2010, 11:52 PM

    ... or are you just happy to see me?

    It's an interesting write-up in support of compiler-related bugs, with a couple examples (something sorely missed in many others).