How do I use Base Class Constructors and Assignment Operators in Derived Classes in C ?

Using Base Class Constructors and Assignment Operator in C

In object-oriented programming, inheritance allows classes to inherit the properties and methods of their base classes. This powerful feature enables code reuse and maintainability. However, handling constructors and assignment operators in inherited classes can be challenging.

Consider a class B with a set of constructors and an assignment operator. The goal is to create an inheriting class D that overrides foo() but retains B's constructors and assignment operator.

Explicit Invocation

One way to achieve this is by explicitly calling the constructors and assignment operators in D. This involves manually invoking the appropriate base class constructor upon creating instances of D and using Base::operator=() to assign values in the assignment operator.

<code class="cpp">class Base {
  // ...
public:
  Base(const Base&) { /*...*/ }
  Base& operator=(const Base&) { /*...*/ }
};

class Derived : public Base {
  int additional_;
public:
  Derived(const Derived& d)
    : Base(d) // dispatch to base copy constructor
    , additional_(d.additional_)
  {
  }

  Derived& operator=(const Derived& d)
  {
    Base::operator=(d);
    additional_ = d.additional_;
    return *this;
  }
};</code>

Implicit Usage

Interestingly, even without explicitly defining constructors and assignment operators, the compiler may generate them automatically. This is the case for classes with straightforward inheritance and minimal customization.

<code class="cpp">class ImplicitBase { 
  int value_; 
  // No operator=() defined
};

class Derived : public ImplicitBase {
  const char* name_;
public:
  Derived& operator=(const Derived& d)
  {
    ImplicitBase::operator=(d); // Call compiler generated operator=
    name_ = strdup(d.name_);
    return *this;
  }
};  </code>

Therefore, when inheriting from a base class that provides a comprehensive set of constructors and an assignment operator, it is possible to use them in the derived class without having to rewrite them, as long as no additional functionality is required in those functions.

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