What About C?

What About C++?

As stated at the beginning of this chapter, C++ does not provide syntactical support for interfaces. However, C++ does provide support for multiple inheritance. Earlier on we described how an interface is very similar to a class with all abstract methods . The problem in Java and C# is a lack of multiple inheritance, which means we can t use this type of class and therefore have to use interfaces.

In C++, thanks to multiple inheritance, we can do something very similar by using a class with all abstract (or pure-virtual) methods. Consider the following C++ class:

 class HTMLSource 
 { 
 public: 
 virtual string GetHTML() const = 0; 
 }; 

Here we have a class with a single pure-virtual function, much like the Java and C# interfaces from earlier. Now, we declare a Student class, derived from the Person class and the HTMLSource class, and provide the GetHTML method:

 class Student: public Person, HTMLSource 
 { 
 public: 
 string GetHTML() 
 { 
 return "<B>" + FirstStr + "&nbsp;"+ LastStr + 
 "</B>&nbspGraduates in " + GraduationYear; 
 } 
 // Portions of class removed for readability 
 }; 

As in Java and C#, we write a function in C++ that takes an HTMLSource object as a parameter and can accept any class with HTMLSource somewhere in its ancestry:

 void ShowHTML( const HTMLSource& Src ) 
 { 
 cout << Src.GetHTML(); 
 }