Sometimes you may need to depart from the conventional wisdom of sound object-oriented design by inspecting the runtime type of an object. Most of the time you should let virtual functions do that job for you, but when writing special-purpose software tools, such as debuggers, database viewers, or class browsers, you'll need to determine type information at runtime. This is where the runtime type identification (RTTI) mechanism becomes useful. RTTI is the topic of Chapter 8.

Multiple inheritance has taken abuse over the years, and some languages don't even support it. Nonetheless, when used properly, it can be a powerful tool for crafting elegant, efficient code. A number of standard practices involving multiple inheritance have evolved over the years, which we present in Chapter 9.

Perhaps the most notable innovation in software development since object-oriented techniques is the use of design patterns. A design pattern describes solutions for many of the common problems involved in designing software, and can be applied in many situations and implemented in any language. In chapter 10 we describe a selected number of design patterns and implement them in C++.

Chapter 11 explains the benefits and challenges of multithreaded programming. The current version of Standard C++ does not specify support for threads, even though most operating systems provide them. We use a portable, freely available threading library to illustrate how C++ programmers can take advantage of threads to build more usable and responsive applications.