Polymorphism is the ability of different objects to react in an individual manner to the same message. This notion was imported from natural languages. For example, the verb "to close" means different things when applied to different objects. Closing a door, closing a bank account, or closing a program's window are all different actions; their exact meaning is determined by the object on which the action is performed. Most object-oriented languages implement polymorphism only in the form of virtual functions. But C++ has two more mechanisms of static (meaning: compile-time) polymorphism: Operator overloading. Applying the += operator to integers or string objects, for example, is interpreted by each of these objects in an individual manner. Obviously, the underlying implementation of += differs in every type. Yet, intuitively, we can predict what results are. Templates. A vector of integers, for example, reacts differently from a vector of string objects when it receives ...
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1 Introduction This paper describes the use of object-oriented software design patterns, as presented in Design Patterns: Elements of Reusable Object-Oriented Software by Gamma et al., within the Microsoft Foundation Class Library (MFC). MFC is used for implementing applications for Microsoft Windows operating systems. Because of the size of the MFC library, a complete analysis would have been beyond the scope of this assignment. Instead, we identified various possible locations for design patterns, using the class hierachy diagram of MFC, and studied the source carefully at these locations. When we did not find a pattern where we expected one, we have documented it anyway, with examples of how the particular problem could have been solved differently, perhaps more elegantly, using design patterns. We have included a brief introduction to MFC in Section 2 , as background information. The analysis has been split into three parts, with one section for each major design pattern ca...
• Why might you need exception handling be used in the constructor when memory allocation is involved?
Your first reaction should be: "Never use memory allocation in the constructor." Create a separate initialization function to do the job. You cannot return from the constructor and this is the reason you may have to use exception handling mechanism to process the memory allocation errors. You should clean up whatever objects and memory allocations you have made prior to throwing the exception, but throwing an exception from constructor may be tricky, because memory has already been allocated and there is no simple way to clean up the memory within the constructor.
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What an empty or null value means depends much on the context. For example, if you think of a website which allows users to register accounts, an empty value could be an anonymous user without an account. In a case like this, you could have a null user object, which represents a user who has not logged in.