Operator Overloading: Extending Functionality of Mathematical Classes in C++, Slides of Computer Science

Download Operator Overloading: Extending Functionality of Mathematical Classes in C++ and more Slides Computer Science in PDF only on Docsity!

Operator Overloading

Member Functions

Operator Overloading

• Function-call notation is cumbersome for certain kinds of classes, especially mathematical classes
• Allows extendable design
• Most appropriate for math classes. eg. Matrix, Vector, etc.
• Gives Operators Class-Specific Functionality
• In-built or Standard Overloading for Basic Numerical Data Types -- + can be used with int, float, doubles
• Analogous to Function Overloading -- operator@ is Used as the Function Name
• 40 Operators can be Overloaded to Give Class-Specific Functionality

Requirements of Overloaded

Operators

• Their Meaning Should be Intuitive -- + Should Mean Addition
• When Appropriate, they Should be Associative -- a + b Should Result in an Object, c of the Same Class
• If these Conditions are Not Satisfied then it is Better to Use Member Functions and Not Operator Overloading
• To use an operator on class objects, that operator must be overloaded - with two exceptions - the assignment operator (=), which performs a member wise copy, and the address (&) operator

Forms of Overloaded Operators

• Member Functions
• Friend Functions
• Free-Standing or Global Functions

Operator Functions (Cont)

• When an operator function is implemented as a member function, the left most (or only in the case of unary operators) operand must be a class object (or a reference to a class object) of operator's class
• If the left operand must be an object of a different class or a built-in type, this operator must be implemented as a non-class member. eg. <<, >> operators

Operator Functions (cont)

• An operator function implemented as a non-

member must be a friend if it needs to access non- public data members of that class.

• The overloaded << operator must have a left

operand of type ostream. Therefore, it must be a non-member function. Also, it may require access to the private data members of the class. Thus, it needs to be a friend function for that class.

Restrictions of Overloaded Operators

• New Operators CANNOT be Created
• Fundamental Data Types (e.g. int ) CANNOT be Overloaded
• Operator Priority CANNOT be Changed
• Operator Associativity CANNOT be Changed
• The arity of CANNOT be changed -- + can Take ONLY TWO Arguments (there is no unary +)
• Two Separate Overloaded Functions (With Different Signatures) can be Created for Operators Which Exist in Pre-fix and Post-fix Form -- ++

Restrictions of Overloaded Operators (Cont)

• Overloaded Operators are NOT IMPLICITLY Associative or Commutative, Even if the Original Operators were Associative or Commutative -- Associativity and Commutativity must be explicitly implemented. For Associativity this means returning an instance of the class.
• Overloading the operator + does not automatically overload related operators (+=, ++, etc). If needed, these related operators must be explicitly overloaded

Binary Overloaded Operators -- Member Functions

• Invocation in Two Ways -- ObjectA @ ObjectB (direct) or ObjectA.operator@(ObjectB) (As a Function) class number{ int n; public: number(int x = 0):n(x){}; number operator+(number ip) {return number (ip.n + n);} }; main() { number a(1), b(2), c, d; //Invocation of "+" Operator -- direct d = a + b; //d.n = 3 //Invocation of "+" Operator -- Function c = d.operator+(b); //c.n = d.n + b.n = 5 }