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How do you access a base class method from a derived class in Cpp?
Use the scope resolution operator (::) to explicitly call the base class method. Note that the base class method must be protected or public in order for a derived class to access it. Private members are only accessible to the class itself and to friends of the class, regardless of whether the derivative uses public, protected or private inheritance. It is quite normal for a base class to provide a "default" implementation for a virtual method for which a derived class may override. Although the derived class will generally provide its own implementation of the method, it may also call the base class method either before, during or after performing its own implementation. The following shows minimal class declarations demonstrating a call to a protected base class method from a derived class override. class base { protected: // accessible to all instances of this class, its friends and its derivatives. virtual void method(){ /* do something */ } }; class derived : public base { public: // full-accessible outside of class. virtual void method(){ /* do something (or do nothing) */ base::method(); // call base class method. /* do something else (or do nothing) */ } };
How do you call a member function of one class in another class using friend function?
class B; // forward declaration. class A { private: void myFunction(B b){b.myFunction();} // Calls private method in b. }; class B { friend void A::myFunction(B b); // Friend function declaration. private: void MyFunction(); };
Can you have virtual constructor in cpp?
A virtual function is a method defined and implemented in a base class that we are expected to override in our derived classes.When we derive a class from a base class, we automatically inherit all the public and protected members of the base class, but we are free to override any and all the methods, including private methods (we can even change the access type if we wish).However, when we override a method in the base class, we can only call that override when we actually have a reference or pointer to the derived class itself. If we cast the reference or pointer to the base class we will end up calling the base class method. This is expected behaviour and is normally fine, but what happens if we have a pointer to a base class but we actually want to call the derived class method? This is particularly important when that call comes from the base class itself. How will it determine its actual type and make the correct call?We could use runtime information within the base class to determine the actual type, but this would break a fundamental rule of encapsulation: a base class should NEVER be concerned about the inner workings of any of its derived classes. If we allow this, we'd be forced to update the base class every time we derived a new class from it. Apart from the performance penalty incurred with accessing runtime information, maintaining the base class code will quickly become unmanageable.That is where virtual functions come in. Even though we are pointing at a base class, when we call a virtual function we actually call the derived class method instead. This is extremely powerful: we are no longer concerned with the actual type of object any more. We can treat the base class as if it were a generic data type, and the compiler will know exactly which version of a function to call regardless of whether the call was made from the base class or not.But what if we want to call the base class method? Simple: make an explicit call to it. We don't need runtime information for this since every derived class is also a base class as well. The only exception is when the virtual function is declared private in the base class. In this case, we are not expected to call the base class method at all (only the base class and friends of the base class can make an explicit call to its private methods).
How do you call base class method using derived class object?
If the base class method is non-private, the derived class can call the base class method implicitly. However, if the derived class overrides or overloads the method, the base class method must be called explicitly. The following demonstrates explicit calls to base class methods: #include <iostream> using namespace std; class Base { public: Base(){} void Foo(){ cout << "Base::Foo" << endl; } }; class Derived : public Base { public: Derived(){} void Foo(){ cout << "Derived::Foo" << endl; Base::Foo(); } }; int main() { Derived derived; derived.Foo(); derived.Base::Foo(); // Explicit call to base class method. return(0); } Output: Derived::Foo Base::Foo Base::Foo
What is function overriding in Java?
Method overriding is similar to method overloading, with a small difference. In overriding, a method in a parent class is overridden in the child class. The method in the child class will have the same signature as that of the parent class. Since the method in the child class has the same signature & name as the method of its parent class, it is termed as overriding. In situations where you may have to explicitly call the parent class method you can use the "super" keyword and for explicitly calling the current objects method you can use the "this" keyword.
