Reading from stdin: performance

Hm - sounds like it could well be related, but compiling/running with that environment variable doesn't seem to affect much for me. Hard to be sure whether it took effect or not, really - the profile looks exactly the same!

Well, they aren't equivalent programs. Your Rust program is allocating a Vec. Your C++ program is not. Why not write equivalent programs?

Also, please try to avoid reaponding to 6 year old threads with your own specific problem. Just open a new thread.