A typical C library contains a struct and some
associated functions to act on that struct. So far,
you've seen how C++ takes functions that are conceptually associated and makes them literally associated by

putting the function declarations inside the scope of the struct, changing the way functions are called for the struct, eliminating the passing of the structure address as the first argument, and adding a new type name to the program (so you don’t have to create a typedef for the struct tag).

These are all convenient – they help you organize your code and make it easier to write and read. However, there are other important issues when making libraries easier in C++, especially the issues of safety and control. This chapter looks at the subject of boundaries in structures.