Undefined behaviour

Question

when i compile
int i = 0;
i = i + i++;
cout << i << endl ;
via gcc and via clang-3.8 i get different results.

Answer 1

i think c/c++ language description has cases where the behaviour is not specified. in the example are rules like: evaluate from left to right, i++ increments i and returns the old value, + is commutative. but they are contradicting.
so i think you can not guarantee the behaviour! it is undefined -