What is the most hard to understand piece of C++ code you know? [closed]

Answer 1

Duff's Device (http://en.wikipedia.org/wiki/Duff%27s_device) give me nightmares:

strcpy(to, from, count)
char *to, *from;
int count;
{
    int n = (count + 7) / 8;
    switch (count % 8) {
    case 0: do { *to = *from++;
    case 7:      *to = *from++;
    case 6:      *to = *from++;
    case 5:      *to = *from++;
    case 4:      *to = *from++;
    case 3:      *to = *from++;
    case 2:      *to = *from++;
    case 1:      *to = *from++;
            } while (--n > 0);
    }
}

Answer 2

Most Boost stuff - the template metaprogramming is bad enough, but when you factor in the workarounds necessary to get it to work on some compilers (*coughborlandcough*), it gets pretty ridiculous. Just try to understand Boost.Bind. Just try.

Answer 3

Binary shift confuses me all the time. An example from the java.util.concurrent.ConcurrentHashMap package:

return ((h << 7) - h + (h >>> 9) + (h >>> 17))

Answer 4

Anything prefixed with:

/* You are not expected to understand this */

Answer 5

I know it's C and not C++ but there is always the the International Obfuscated C Code Contest. I have seen some code there that would make your head spin.