In principle the C++ standard does define a subset of its standard library which is available in Freestanding environments (ie without an operating system).
In practice what is actually available and whether it works satisfactorily varies considerably more than for the hosted environments. Almost everything is up for grabs and so you probably can't rely on the standard much. Your compiler vendor probably couldn't care less what the standard says anyway.
In practice what is actually available and whether it works satisfactorily varies considerably more than for the hosted environments. Almost everything is up for grabs and so you probably can't rely on the standard much. Your compiler vendor probably couldn't care less what the standard says anyway.