FWIW I’ve seen space FSW instances where both std:: was allowed and forbidden. One instance was soft real-time FSW running on a customized Linux. Most (sane) C++ was allowed, exceptions were not disabled, just disallowed, std:: was allowed during initialization, but not past that, memory allocation was only allowed during initialization as well, although a stray allocation at runtime was only fatal in testing, not during flight. It was logged in both cases and considered a critical issue. PR reviews had strict checklist rules regarding allowed syntax/features. It was very productive using all of the necessary C++ features, within reason, to write code.