Chapter 20. Smart Pointers

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Memory is a resource that is normally explicitly managed in C++ programs. This management involves the acquisition and disposal of blocks of raw memory.

One of the more delicate issues in managing dynamically allocated memory is the decision of when to deallocate it. Among the various tools to simplify this aspect of programming are so-called smart pointer templates. In C++, smart pointers are classes that behave somewhat like ordinary pointers (in that they provide the dereferencing operators -> and * ) but in addition encapsulate some memory or resource management policy.

In this chapter we develop smart pointer templates that encapsulate two different ownership models ”exclusive and shared:

• Exclusive ownership can be enforced with little overhead, compared with handling raw pointers. Smart pointers that enforce such a policy are useful to deal with exceptions thrown while manipulating dynamically allocated objects.

• Shared ownership can sometimes lead to excessively complicated object lifetime situations. In such cases, it may be advisable to move the burden of the lifetime decisions from the programmer to the program.

The term smart pointer implies that objects are being pointed to. Alternatives for function pointers are subject to different issues, some of which are discussed in Chapter 22.

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