CSC/ECE 517 Fall 2011/ch1 1i lj

CSC/ECE 517 Fall 2010/ch1 1i lj

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Overriden Method

Method overriding[1], in object oriented programming, is a language feature that allows a subclass to provide a specific implementation of a method that is already provided by one of its superclasses. The implementation in the subclass overrides (replaces) the implementation in the superclass.

C++

In native C++, a derived class function having the same name and parameters as a base class virtual function will *always* override it. In C++/CLI you have the option of using the new contextual keyword to specify whether you want to override a base class function or hide it. Example:

ref class Base
{
public:
    virtual void Goo()
    {
        Show("Base::Goo");
    }
    
    virtual void Boo()
    {
        Show("Base::Boo");
    }
    
    virtual void Doo()
    {
        Show("Base::Doo");
    }
};

ref class Derived : Base
{
public:
    //Overrides Base::Goo

    virtual void Goo()
    {
        Show("Derived::Goo");
    }
    
    //Overrides Base::Boo as above

    virtual void Boo() = Base::Boo
    {
        Show("Derived::Boo");
    }
    
    //Hides Base::Doo

    virtual void Doo() new
    {
        Show("Derived::Doo");
    }
};

Here's some sample code that invokes the above methods on a Base handle referencing a Derived object.

void _tmain()
{
    Base^ r = gcnew Derived();
    r->Goo();
    r->Boo();
    r->Doo();
}

You'll get the following output :

Derived::Goo
Derived::Boo
Base::Doo

C++/CLI

Introduction When Microsoft brought out the Managed Extensions to C++ with VS.NET 7, C++ programmers accepted it with mixed reactions. While most people were happy that they could continue using C++, nearly everyone was unhappy with the ugly and twisted syntax offered by Managed C++. Microsoft obviously took the feedback it got very seriously and they decided that the MC++ syntax wasn't going to be much of a success. On October 6th 2003, the ECMA announced the creation of a new task group to oversee development of a standard set of language extensions to create a binding between the ISO standard C++ programming language and Common Language Infrastructure (CLI). It was also made known that this new set of language extensions will be known as the C++/CLI standard, which will be supported by the VC++ compiler starting with the Whidbey release (VS.NET 2005). Renamed Overriding: Native C++ insisted that the derived class method name must match the name of the base class virtual method that it is overriding. C++/CLI allows us to have a derived class method override a base class virtual method even if the derived class method name does not match the base class method name. Of course the method signatures must be equivalent. The following code snippet should make things clear.