Class Hierarchies
Figure 2 – Portal classes 
Figure 3 – Wrapper classes 
The RWxmsg, RWInternalErr, and RWExternalErr classes shown in Figure 4 are included in the Essential Tools Module.
Figure 4 – Data-handling and error-handling classes
The istream, streambuf, and ostream classes shown in Figure 5 are included in the Standard C++ Library Module.
Figure 5 – I/O services in the Networking package
