Rules for Overloading Operators

1. Only existing operators can be overloaded. New operators cannot be created.
2. The overloaded operator must have at least one operand that is of user defined type.
3. The basic meaning of an operator cannot be changed. That is the plus operator cannot be used to subtract one value from the other.
4. Overloaded operator follow the syntax rules of the original operators. They cannot be overridden.
5. There are some operators that cannot be overloaded. They are Size of, .  ,: :,?:.
6. Friend function cannot be used to overload certain operators ( = ,( ) ,[ ] ,->).However member functions can be used to overload them.
7. Unary operators, overload by means of a member function, take no explicit arguments and return no explicit values, but, those overloaded by means of a friend function, take one reference argument.
8. Binary operators overloaded through a member function take one explicit argument and those which are overloaded through a friend function take two explicit arguments.
9. When using binary operator overloaded through a member function, the left hand operand must be an object of the relevant class.
10. Binary arithmetic operators such as +,-,*,and / must explicitly return a value. They must not attempt to change their own arguments.

Example

#include <iostream.h>

#include <string.h>

class Product{

public:

         Product() : name(NULL) {}

         Product(char* str);

         const Product& operator=(const Product& );

         void Print() { cout << "Product: " << name << endl; }

         const char* getProduct() const { return name; }

private:

   char * name;

};

Product :: Product(char* str){

         name = new char[strlen (str)+1];

         strcpy (name, str);

}

const Product& Product :: operator=(const Product& p){

         delete [] name;

         name = new char[strlen(p.getProduct())+1];

         strcpy(name, p.getProduct());

         return *this;             // This will allow assignments to be chained

}

int main(){

         Product p1("Hammer"), p2("Shovel"), p3;

               p3 = p2;            // p2 and p3 will have equivalent name strings

               p2.Print();

               p3.Print();

               p3 = p2 = p1;   // p1, p2, and p3 will have equivalent name strings                 

               p1.Print();

               p2.Print();

               p3.Print();

         return 0;