| UB has 2 very different implications: 1. It means that even if your program happens to work, it can't be portable 2. It means that even if your program happens to work today, it might stop working tomorrow when you add some new code, when you change some compiler flags, or when you do even a minor compiler upgrade Of course, a compiler can't address 1. However, a compiler can very much address item 2. If Microsoft were to say "in MSVC, we define integer overflow to wrap", then they would guarantee that `INT_MAX + 1` will produce `INT_MIN` regardless of any optimization settings, any compiler upgrades, any other changes to the code. Of course, compiling the exact same program with Clang or GCC might cause it to crash or corrupt memory or anything else - but as long as you stuck with MSVC, your program would have perfectly defined semantics. This is similar to using compiler extensions or intrinsics - they are not portable and not defined by the standard, maybe even explicitly defined to NOT be supported per the standard (such as variable length arrays in C++ in GCC), but they are nevertheless perfectly safe as long as you stick to your chosen compiler. Edit to add: the integer overflow example is not just a theoretical possibility - lots of C++ compilers provide the `-fwrapv` flag; when using that flag, signed integer overflow is no longer UB for that program, it is defined just the same as unsigned integer overflow. |