How Do Default Parameter Values Behave in C Virtual Functions and Inheritance?

Virtual Functions and Default Parameter Usage

In C , virtual functions allow derived classes to override their base class implementations with their own specialized behavior. However, when it comes to default parameter values, the rules for inheritance differ from regular parameters.

Default Parameter Values in Base Classes

Virtual functions can have default parameter values specified in their base class declaration. These defaults are not inherited by derived classes. Instead, derived classes must specify their own default values or omit them altogether.

Default Parameter Selection

When calling a virtual function through a derived class object, the default parameter values used are determined by the static type of the pointer or reference used to call the function. If the call is made through a base class object or pointer, the base class's default values are used. Conversely, if the call is made through a derived class object or pointer, the derived class's default values are used.

Example

Consider the following example:

struct Base {
  virtual void f(int a = 7);
};

struct Derived : public Base {
  void f(int a = 9);
};

If we call f() through a Base pointer, it will use the default value defined in Base, which is 7. However, if we call f() through a Derived pointer, it will use the default value defined in Derived, which is 9.

Cross-Platform Considerations

While the C 03 and C 11 Standards specify the behavior described above, different compilers may handle default parameter inheritance differently. It is recommended to always specify default parameter values explicitly in derived classes to avoid any potential discrepancies.

Conclusion

Virtual functions can have default parameters, but these defaults are not inherited by derived classes. The default values used in a virtual function call are determined by the static type of the object through which the function was called, ensuring that derived classes can customize their own default behavior as needed.

The above is the detailed content of How Do Default Parameter Values Behave in C Virtual Functions and Inheritance?. For more information, please follow other related articles on the PHP Chinese website!