Obscure C code (was Re: Excessive optimization)

A[i++] = i++; I can't quote chapter and verse, but I'm fairly sure the standard will say that the result of that assignment is undefined. In pre-standard C, it is also undefined, but for a different reason. Many programmers would say "I would never write code like that", but I've seen statements like that creep into code as a result of cut-and-paste or global-search-and-replace operations that weren't carefully checked. It's also quite possible when writing complex expressions to come up with things like that which are not necessarily obvious to casual inspection. It is good that many compilers will detect these things and generate warnings. When I have the power to do so, I generally treat warnings from the compiler as fatal errors requiring a fix, and not acceptable in released code.