I'm almost sure this is undefined behavior! It may break on you at unexpected moments (such as when you change optimization options or compilers). I'm certain

I'm almost sure this is undefined behavior! It may break on you at unexpected moments (such as when you change optimization options or compilers). I'm certain it was undefined, but perhaps some new standard is stricter (I don't think so, however). See http://en.wikipedia.org/wiki/Sequence_point http://en.wikipedia.org/wiki/Sequence_point In essence there's no guarantee the read from the first reference to b will occur before the write to the second reference. Edit: a quick skim of C++11 changes doesn't seem like it includes any changes here, just some rewording and clarification: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2239.html http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n223...