I’m not defending the implementation (I hate most of std::iostream), just that "\n" is not exactly equivalent so switching to that may cause surprising behavior

I’m not defending the implementation (I hate most of std::iostream), just that "\n" is not exactly equivalent so switching to that may cause surprising behavior and create problems. Auto-flush has its uses. If the main purpose of a program is to generate output then it ought to know what it’s doing anyway and know how to avoid poor performance. For most programs, I’d say that Unix rules of thumb apply: if you are already trying to be “silent on success”, your program will either print nothing or maybe an error or two and not have to worry about print performance. If your program might only print one error and that doesn’t even show up because a flush didn’t happen before a crash, there is a big problem.