alt Hacker NewsI don’t work a ton with C, but I wonder how C programmers keep track of what behavior is and is not defined. It seems like there are many possible edge cases.
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We get by on a combination of matching patterns (any pointer cast gets a lot of scrutiny, for example), compiler warnings, tools like UBSan, debugging when things go wrong, and sheer dumb luck.
Having an understanding of how the code gets transformed into machine code helps. For this case, there's the basic idea that `a++` will boil down to three basic conceptual operations: fetch, add, and store, and those can be potentially interleaved with other parts of the statement. In something like `a++ + ++b` the interleaving doesn't affect the outcome no matter how it's done. In `a++ + ++b` the interleaving can affect the outcome, and that's your sign that something might be wrong.
Any memory safety issue in C code had to involve UB at some point. And you can see how prevalent those are, and deduce how not-particularly-great we are at keeping track of UB.
They don't really. In fact there are many things that are technically UB but are so common that compilers can't really treat them as UB. E.g. type punning via unions.
They don't. In the culture some kinds of undefined behaviour are taken seriously and some aren't. If you want to write code that "works", you emulate what popular performance benchmarks do (whether their code is undefined according to the standard or not), since those are the thing that C compiler developers actually care about.