C + + Virtual base class

Naming conflicts can easily arise when multiple inheritance occurs, and if we carefully name the member variables and member functions in all classes as different names, it is still possible for a naming conflict to occur, such as a very classic diamond inheritance hierarchy. Class A derives from Class B and Class C, and Class D inherits from Class B and Class C, at which time the member variables and member functions in Class A inherit into Class D into two parts, one from a derived B and then the other from a derivation C, and then the derivation of D.

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This example is a typical diamond inheritance structure, the member variables in Class A and the member functions inherit into Class D will produce two copies, such a naming conflict is very tricky, through the domain resolution operator has been unable to distinguish the specific variables. For this reason, C + + provides virtual inheritance in this way to resolve the naming conflict problem. Virtual inheritance requires only the virtual keyword to precede the inherited attribute.

Example 2:

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In this case, Class B and Class C are both inherited and class A are virtual, and after doing so, Class D will only get a copy of the data from Class A. In the main function of this example, the object test of Class D is defined, and then the SETX and GETX member functions are called indirectly from Class A, since B and C inherit from Class A with virtual inheritance, so calling Setx and getx through D does not have a naming conflict problem. Because Class D only gets a copy of A's data.

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C + + Virtual base class