【導(dǎo)讀】C++是目前所使用的眾多編程語言中的一種。總會(huì)有新的語言不斷出現(xiàn)？個(gè)編程語言對(duì)基本的機(jī)器結(jié)構(gòu)有很大的依賴性。在一個(gè)高水平的環(huán)境編寫，因而是程序員可以不必了解機(jī)器的細(xì)節(jié)。有很多語言可以訪問大型數(shù)據(jù)庫，格式化。變化的大氣層狀況，下棋和繪制電路圖。每一個(gè)問題都需要不同的數(shù)據(jù)結(jié)構(gòu)和算法。程序語言作為一種工具幫助我們解決這些問題。然而，并不是一種程序語言可以最。使用多種多樣的語言建立不同的設(shè)計(jì)方案。個(gè)范例可以被認(rèn)為是一個(gè)模式或者一個(gè)框架來設(shè)計(jì)和描述軟件結(jié)構(gòu)。合語言，如C++，綜合了兩到三種范例。C++包括了命令和程序范例的特性，例如，達(dá)式，條件分枝控制執(zhí)行流。一個(gè)C++的類既包括共有的部分，又包。C++提供了關(guān)鍵字來說明類中哪些成員是不可見的，哪些部分是其公共接口。時(shí)，它的構(gòu)造函數(shù)初始化其在內(nèi)存的值。我們不可能對(duì)用戶完全的隱藏操作的細(xì)節(jié)。C++無法提供一個(gè)使所有細(xì)節(jié)完全排

　　

【正文】 vate inheritance. For example, a stack can be implemented using an array. We can either use the stack as a data member (position) or derive the stack class from the array class using private inheritance. It is also possible to use inheritance to achieve a containership relationship between two classes. Private inheritance is used when the inheritance is not part of the interface。 the base class is an implementation detail. Under private inheritance, the public and protected parts of the base class bee part of the private part of the derived class. Users of the derived class cannot access any of the base class interface. However, member functions of the derived class are free to use the public and private parts of the base class. When used this way, users cannot write code that depends on the inheritance. This is a powerful way of preserving your ability to change the implementation to a different base class. One other form of inheritance, which is very rarely used is protected inheritance. Protected inheritance is also used to implement HASA relationships. When protected inheritance is used, the public and protected parts of the base class bee protected in the derived class. So, you may wish to use protected inheritance when the inheritance is part of the interface to derived classes, but not part of the interface to the users. A protected base class is almost like a private base class, except the interface is known to derived classes. 12 It is best to use position where possible. In cases where you must override functions in a base class then by all means use inheritance. Only use public inheritance if your derived class is indeed a specialization of the base class, otherwise, private inheritance should be used. Needlessly using inheritance makes your system harder to understand. In summary, a class specifies two interfaces: one to the users of the class (the public interface) and another to implementers of derived classes (the union of public and protected parts). Inheritance works almost identically. When the inheritance is public, the public interface of the base class bees part of the public interface to users of the derived class. When the inheritance is protected, the public and protected parts of the base class are accessible to the member functions (the implementation) of the derived classes, but not to general users of the derived classes. Finally, when inheritance is private, the public and protected parts of the base class are only accessible to the implementer of the class, but not to users or derived classes. POLYMORPHISM in C++. Polymorphism is the last of the three fundamental primitives of objectoriented programming and the most important. Together with inheritance, polymorphism brings the most power, in terms of runtime flexibility, to objectoriented programming. Polymorphism, which means many forms, provides a generic software interface so that a collection of different types of objects may be manipulated uniformly. C++ provides three different types of polymorphism: virtual functions, function name overloading, and operator overloading. The virtual function mechanism can only be invoked through the use of a base class reference or pointer. Recall that a base class pointer can point to an object of the base type or an object of any type that is derived from the base class. Virtual functions are also used to implement the logic gate hierarchy .The class gate is an abstract base class at the root of the inheritance hierarchy. A class is considered abstract when some of its virtual member functions do not have an implementation. These functions are assigned to be zero in the class classes must provide implementations for them. Another form of polymorphism found in C++ is function overloading. A function is said to be overloaded when it is declared more than once in a program. Overloading allows a set of functions that perform a similar operation to be collected under the same name. When there are several declarations of the same function, the piler determines which function should be called by examining the return type and argument signature of the function call. 13 When we define new data types, it is often useful to define standard operations that are found in similar types. For example, a plex type also has addition and subtraction defined for it. We can use operator overloading so that the addition (`+39。) and subtraction (`39。) operators work for plex objects just as they do for ints and floats. Operators are defined in much the same was as normal C++ functions and can be members or nonmembers of a class. Operators take one or two arguments and are called unary and binary operators accordingly. In C++, a member operator function is defined like an ordinary member function, but the name is prefixed with the keyword operator. C++ places a number of restrictions on operator overloading. Only the predefined set of C++ operators may be overloaded. It is illegal to define a new operator and then overload it. You cannot turn a unary operator into a binary operator or vice versa. Also, the following operators cannot be overloaded: scope operator (`::39。), member object selection operator (`.*39。), class object selector operator (`.39。), and the arithmetic if operator (`?:39。). In the last two issues of ObjectiveViewPoint we have looked at how C++ supports the objectoriented paradigm.