How to Implement Virtual Operator Overloading in C ?

Virtual Operator Overloading

Background

In C , operators can be overloaded for custom data types, providing tailored behaviors. However, virtual methods, allowing for polymorphic behavior, cannot be directly used for operator overloading.

The Issue

Consider the desire to create a virtual operator << to customize printing for a class Advertising. Attempts to define a virtual friend operator << result in a compiler error, stating that only member functions and bases can be virtual.

The Solution: Indirection

To circumvent this limitation, the operator << cannot be made virtual directly. Instead, a new virtual member function print can be added to the Advertising class. The << operator can then be redefined as a free function:

<code class="cpp">class Advertising {
public:
    virtual void print(ostream& os) const;
};

ostream& operator<< (ostream& os, const Advertising& add) {
    add.print(os);
    return os;
}</code>

In this approach, the print member function can be overridden in subclasses to customize printing behavior, while the << operator maintains the correct parameter order for convenient use.

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