Shulou(Shulou.com)06/02 Report--

Today, I would like to talk to you about how to analyze the inheritance relationship of C++, which may not be well understood by many people. in order to make you understand better, the editor has summarized the following for you. I hope you can get something from this article.

For users and scholars who have come into contact with C++ class inheritance for many times, but first of all to fully understand the nature of C++ class inheritance, let's first talk about what is C++ class. The so-called C++ class: a class is a blueprint or prototype that defines variables and methods of all objects of the same class.

1. Public

From a semantic point of view, public inheritance is a kind of interface C++ class inheritance, according to the relationship in the object-oriented, that is, the subclass can replace the parent class to complete the behavior declared by the parent class interface, that is, it must comply with the "Liskov substitution (LSP)". At this time, the subclass can be automatically converted into the interface of the parent class to complete the interface transformation. Syntactically, public inheritance retains the visibility of the members of the parent class (including functions and variables, etc.), that is, if a function in the parent class is public, it is still public after the subclass inherits.

2. Protected

From a semantic point of view, protected inheritance is a kind of implementation inheritance, according to the relationship in object-oriented, that is, the subclass can not replace the parent class to complete the behavior declared by the parent class interface, that is, it does not conform to the "Liskov substitution principle (LSP)". At this time, the subclass can not be automatically converted into the interface of the parent class.

Even through type conversion (static_cast and dynamic_cast), you get a null pointer. Syntactically, protected inheritance changes the members of public visibility in the parent class to protected visibility, which is equivalent to the introduction of protected members in the subclass, so that the protected and public members of the parent class can also be called in the subclass, and the protected and public members of the parent class inherited by protected can also be called by the subclass of the subclass.

3. Private

From a semantic point of view, private inheritance is an implementation of C++ class inheritance, according to the relationship in object-oriented, that is, the subclass can not replace the parent class to complete the behavior declared by the parent interface, that is, it does not comply with the "Liskov substitution principle (LSP)". At this time, the subclass can not be automatically converted into the interface of the parent class.

Even through type conversion (static_cast and dynamic_cast), you get a null pointer. Syntactically, private inheritance changes the members of public and protected visibility in the parent class to private visibility, so that although the protected and public members of the parent class can also be called in the subclass, members of the parent class inherited by private can no longer be called in the subclass of the subclass.

Class CSample1 {protected: void printProtected () {} public: void printPublic () {}}; class CSample2: protected CSample1 {}; class CSample3: public CSample2 {void print3 () {printProtected (); printPublic ();}}

In object-oriented theory, there are two concepts: interface and implementation, so there are two kinds of relationship between interface inheritance and implementation inheritance. Protected and private are used in the implementation of inheritance, in fact, protected and private do not form two different inheritance categories when constraining inheritance, but are only designed to facilitate the transfer of C++ methods.

In fact, in java, which has more stringent object-oriented requirements, there is no inheritance, so he must complete this concept through delegation. If you are familiar with java, you will understand that if an object wants to use the interface function of another object, and it cannot play the role played by the object, it will be done through delegation.

In this way, you must include a delegate object in the object, through the object call syntax to complete the function; in C++, you can use protected and private inheritance to complete the delegate relationship in java (of course, C++ can also form an object delegate relationship), then protected inheritance allows delegation to be passed (that is, it is called by multiple subclasses), and private inheritance does not allow delegation to be passed.

After reading the above, do you have any further understanding of how to analyze the inheritance relationship of C++ class? If you want to know more knowledge or related content, please follow the industry information channel, thank you for your support.

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