4 ms·

It's not just the C spec you've got to watch. I saw a wonderful bug last week where the author hadn't spotted that write(2) returned a ssize_t, not a size_t (o

• nitrogen 14y ago
  How did the bug manifest itself? You can store 0xffffffff(ffffffff) in a 32(64)-bit unsigned int, or a 32(64)-bit signed int. In the one case you'll get UINT_MAX, -1 in the other, but they should compare as equal. If you have -Wextra turned on, gcc will give a warning, though. Here's some sample C code tested on a 32-bit Linux system: #include <stdio.h> int main(int argc, char *argv[]) { unsigned int val1 = 0xffffffff; printf("val1 == -1: %d\n", val1 == -1); return 0; } The result: val1 == -1: 1
  • mikeash 14y ago
    It works for == -1, but not for < 0, which is a common way to check for error returns from UNIX calls. Any decent compiler should warn that such a check is always false, but people don't always pay attention to that stuff....
    • regularfry 14y ago
      Got it in one :-)
    • nitrogen 14y ago
      C is my absolute favorite language, and as such, I learned a long time ago to pay very close attention to compiler warnings and Valgrind memory errors.
      • mikeash 14y ago
        Sadly, a lot of people have never learned this valuable lesson, and happily build their code with hundreds or even thousands of warnings.