With C, you are not 100% sure that ur code will work. You have to verify and extensively test it. With C++ you have some very vague guarantees about ur code but you can easily transition from C and even have some interesting type safety like mp-units. with Rust, you have some good guarantees that ur code wont have UAF, will be threadsafe, etc etc and you can probably invent some interesting typesafety like mp-units.

In all 3, you gotta verify [frama-C, astree,bedrock, the many projects working on rust, esp the coq one] and extensively test it.

But by default, all 3 provide a different level of gurantees