Why would I include iostream and ostream separately? [duplicate]

Answer 1

iostream explicitly includes istream and ostream (C++0x requires this, and the gnu libstdc++ version does this), so ostream is technically unnecessary

for future reference:

fstream contains the declaration for fstream (file streams),

sstream contains the declaration for stringstream (string streams)

iostream declares the standard i/o facilities (e.g. cin, cout, ...)

iosfwd is the standard header that forward-declares the major types.