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

Answer 1

This is well known but still impressive way to swap two integers without creating temp variable:

// a^=b^=a^=b;     // int a and int b will be swapped
// Technically undefined behavior as variable may only 
// be assined once within the same statement.
// 
// But this can be written correctly like this.
// Which still looks cool and unreadable ;-)

a^=b;
b^=a;
a^=b;