Operation Overloading.

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Mary Watts
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1 Operation Overloading

2 Operation Overloading Operation overloading means, same operation has different response to different objects We have seen function overloading distance(int, int); distance(point); //from origin distance(point, Point); Below are examples of operator overloading x + y; //where x and y are double object s1 + s2; //where s1 and s2 are string objects c1 + c2; //where c1 and c2 are complex objects

3 Operator Overloading Operator based expressions are much easier to read; compare a + b * c with plus(a, times(b, c)) Operator Overloading is a powerful tool in C++, but at the same time could be quiet error prone, and confusing C++ allows programmers to give different meaning to operator; and this, providing a new meaning to an operator is called operator overloading

4 Suppose, you want to have a class Complex such that following client executes as expected What operations you need to define for this? Four operator: >>, +, <<, = You don t have to overload =, as default copying in C++ suffices for this class; Others we need to. We have not learned so far how to write such class

5 Another Client program, doing same functionality, but uses different class interface This Complex class probably you can write? However, users of the class would probably appreciate previous interface; that uses operators rather than functions To have operator based interface you need to overload appropriate operator

6 Exercise Given this (side by) definition of class Implement following function A global function: Complex add(const Complex&, const Complex&); A member function to class Complex: Complex add(const Complex&);

7 add as global function Here is how you would use this function to add two Complex numbers Complex c1, c2, c3; c1.read( cin ); c2.read( cin ); c3 = add(c1, c2);

8 add as member function Here is how you would use this function to add two Complex numbers Complex c1, c2, c3; c1.read( cin ); c2.read( cin ); c3 = c1.add( c2 );

9 Two solution for adding two complex numbers Both are doing job. How does that matter to you; Global function can not access private data members of the class; while member function can

10 Operator Overloading Operators, however can not be defined new meaning for primitive data types; When we define overloading, one of the operator has to be of user defined types Operators in C++ can be overloaded in two ways- They can be defined as global functions, or can be defined as member functions.

11 Operator Overloading as global functions For this, you define a global function whose name is operator followed by the operator symbol, and operands are parameters to it; left operand as first parameter while right operand as second parameter; as shown below -

12 When you have this function defined, you can write following expression: c1 + c2 Compiler interprets this expression as function call operator+(c1, c2) The function Implementation defines actions that needs to be performed when such expression encounters

13 Overload the operator to add objects of two different types Suppose, you want to write an expression c ; for this you may have to write another function, which takes, second parameter of other type, say double in this case -

14 Operator Member function When define operator+ as member function, and write expression: c1 + c2 Then, the compiler would interprets it as function call c1.operator+(c2)

15 Defines operator+ such that a double can be added to a Complex object: c Then, the compiler would interprets it as function call c1.operator+(5.6)

16 Operator Overloading When your write expression: a + b where a, b are objects of some class; suppose classes A and B respectively A and B could be same class or two different classes; normally are from same class though Compiler attempts to translate this expression to a function call and binds it to appropriate function definition, if finds, otherwise raises compilation error Note that, right now, we are talking about binary operator only

17 Operator Overloading When compiler finds this expression, first it looks for a member function operator+ in class A, if finds, then translates above expression to a.operator+(b) If not then looks for a global function operator+, having two parameters of type A and B respectively, if finds then translates expression a+b to operator+(a,b) If still does not find; compiler raises error: no match for 'operator+' in a + b'

18 Thanks

Operation Overloading.

Operation Overloading. Operation Overloading pm_jat@daiict.ac.in Recap: Why do we need Operator Overloading? Operator based expressions are more readable: Compare a + b * c with plus(a, times(b, c)) Recap: What is Operator Overloading?