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Tip of the Day
Language: C++
Expertise: All
Jul 31, 1998



Building the Right Environment to Support AI, Machine Learning and Deep Learning

Simulating Inheritance of Assignment Operator

As opposed to base class' constructor and destructor, which are automatically invoked from the derived class' constructor and destructor respectively, a user-defined assignment operator defined in a base class is overridden - rather than being extended - when re-defined in a derived class. In order to extend the assignment operator in a derived class, one has first to invoke the base's assignment operator explicitly, and then add the assignment operations required for the derived class.
class C {
char *p; 
	enum {size = 10}; //size serves as a constant
	const char * Getp() const {return p;}
	C() : p ( new char [size] ) {}
C& operator = (const C& other) {
if (this != &other) 
		strcpy(p, other.Getp() ); 
		return *this;} 
//...destructor and copy constructor
class D : public C {
	char *q;
	const char * Getq() const {return q;}
	D(): q  ( new char [size] ) {}
D& operator = (const D& other) 
		if (this != &other)  
		C::operator=(other);  //first invoke base's assignment operator explicitly
		strcpy(q, (other.Getq()));  //add extensions here
		return *this;
//...destructor and copy constructor
Danny Kalev
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