Can C Virtual Functions Be Overridden with Different Return Types?

Overriding Virtual Functions with Different Return Types in C

One of the key features of virtual functions in C is the ability to override them in derived classes to provide specialized implementations. However, it's not always clear if it's permissible to use a different return type in the overriding function.

In most cases, the answer is yes, provided the return type complies with certain constraints. Specifically, the return type must be covariant with the original return type. Covariance means that the return type of the overriding function must be a subtype of the original return type or implicitly convertible to it.

Consider the following example:

class Base {
public:
    virtual ~Base() {}

    virtual Base* clone() const = 0; // pure virtual function
};

class Derived: public Base {
public:
    virtual Derived* clone() const {
        return new Derived(*this);
    }
};

In this example, the Base class defines a pure virtual function clone that returns a Base*. The Derived class overrides clone and returns a Derived*. This is allowed because Derived* is a subtype of Base*.

In general, any function's return type is not considered part of its signature in C . Therefore, you can override member functions with any return type as long as it satisfies the covariance rule. This allows derived classes to provide more specific implementations of virtual functions without violating contract requirements.

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