Item 1: View C++ as a federation of languages
In the beginning, C++ was just C with some object-oriented features tacked on. Even C++'s original name, "C with Classes," reflected this simple heritage.
As the language matured, it grew bolder and more adventurous, adopting ideas, features, and programming strategies different from those of C with Classes. Exceptions required different approaches to structuring functions (see Item 29). Templates gave rise to new ways of thinking about design (see Item 41), and the STL defined an approach to extensibility unlike any most people had ever seen.
Today's C++ is a multiparadigm programming language, one supporting a combination of procedural, object-oriented, functional, generic, and metaprogramming features. This power and flexibility make C++ a tool without equal, but can also cause some confusion. All the "proper usage" rules seem to have exceptions. How are we to make sense of such a language?
The easiest way is to view C++ not as a single language but as a federation of related languages. Within a particular sublanguage, the rules tend to be simple, straightforward, and easy to remember. When you move from one sublanguage to another, however, the rules may change. To make sense of C++, you have to recognize its primary sublanguages. Fortunately, there are only four:
Keep these four sublanguages in mind, and don't be surprised when you encounter situations where effective programming requires that you change strategy when you switch from one sublanguage to another. For example, pass-by-value is generally more efficient than pass-by-reference for built-in (i.e., C-like) types, but when you move from the C part of C++ to Object-Oriented C++, the existence of user-defined constructors and destructors means that pass-by-reference-to-const is usually better. This is especially the case when working in Template C++, because there, you don't even know the type of object you're dealing with. When you cross into the STL, however, you know that iterators and function objects are modeled on pointers in C, so for iterators and function objects in the STL, the old C pass-by-value rule applies again. (For all the details on choosing among parameter-passing options, see Item 20.)
C++, then, isn't a unified language with a single set of rules; it's a federation of four sublanguages, each with its own conventions. Keep these sublanguages in mind, and you'll find that C++ is a lot easier to understand.
Things to Remember