Quote Originally Posted by Daved
It was actually "standard" for many years before there was a standard
I can see why the first "standard" is in quotes... anyway, as far as the current standard is concerned, iostream.h is apparently only mentioned in one of the appendixes as being provided as a coutesy for all the existing code that includes it. It is, however, not standard.

There actually are small differences between the two libraries that you may or may not encounter when using it. They are listed here.