Chapter Summary

Most of C++ is applicable to a wide range of problemsfrom those solvable in a few hour's time to those that take years of development by large teams. Some features in C++ are most applicable in the context of large-scale problems: exception handling, namespaces, and multiple or virtual inheritance.

Exception handling lets us separate the error-detection part of the program from the error-handling part. Section 6.13 (p. 215) introduced exception handling and this chapter completes our coverage of exceptions. When an exception is thrown, the current executing function is suspended and a search is started to find the nearest catch clause. Local variables defined inside functions that are exited while searching for a catch clause are destroyed as part of handling the exception. The fact that objects are destroyed gives rise to an important programming technique known as "resource allocation is initialization" (RAII).

Namespaces are a mechanism for managing large complex applications built from code produced by independent suppliers. A namespace is a scope in which objects, types, functions, template, and other namespaces may be defined. The standard library is defined inside the namespace named std.

Names in a namespace may be made available to the current scope one at a time via a using declaration. Alternatively, but much less safely, all the names in a namespace may be brought into the current scope via a using directive.

Conceptually, multiple inheritance is a simple notion: A derived class may inherit from more than one direct base class. The derived object consists of the derived part and a base part contributed by each of its base classes. Although conceptually simple, the details can be more complicated. In particular, inheriting from multiple base classes introduces new possiblities for name collisions and resulting ambiguous references to names from the base part of an object.

When a class inherits from more than one immediate base class, it is possible that those classes may themselves share another base class. In cases such as this, the intermediate classes can opt to make their inheritance virtual, which states a willingness to share its virtual base class with other classes in the hierarchy that inherit virtually from that same base class. In this way there is only one copy of the shared virtual base in a subsequently derived class.