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C++ Operator Overloading

C++ Operator Overloading. Gordon College CPS212. Function overloading. Function overloading enables writing more then one function with the same name but different signature. int my_func(int a, int b) { return(a * b); } int my_func(int a, int b, int c) { return( a * b * c); }

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C++ Operator Overloading

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  1. C++ Operator Overloading Gordon College CPS212

  2. Function overloading Function overloading enables writing more then one function with the same name but different signature. int my_func(int a, int b) { return(a * b); } int my_func(int a, int b, int c) { return( a * b * c); } my_func(2,4); my_func(2,4,6);

  3. Function overloading int Add(int nX, int nY) { return nX + nY; } double Add(double dX, double dY) { return dX + dY; } int Add(int nX, int nY, int nZ) { return nX + nY + nZ; } ERROR (signature must be unique in some way) int GetRandomValue(); double GetRandomValue();

  4. Operator overloading • Some languages allow only function (method) overloading - such as Java. • However, on a primitive level all languages use operator overloading to some degree. • Consider 4 + 6 3.4 + 5.6 “Cows “ + “can jump”

  5. Operator overloading • Operator overloading doesn’t add power to code - it essentially enhances the coding experience (efficiency for the programmer) • Adds logical depth to ADTs: • If there is a new type called “BirthdayList”, shouldn’t it possible to add, substract, compare lists and display using intuitive operators? listA == listB listA + Jim listA - Marvin cout << listA

  6. Operator overloading • The only operators that cannot be overloaded are :: (scope resolution), . (member selection), and .* (member selection through pointer to function).

  7. Operator overloading • FRIEND (free – yet is associated with class – inline or external function) friendconstPointoperator+ (constPoint&, constint&); friendostream & operator<<( ostream&, constPoint &); • CLASS constPoint& operator= (constPoint&); • FREE constPointoperator- (constPoint&, constPoint&); Within Class Definition

  8. Operator overloading • FRIEND (free that is allowed access to private variables of class – Friend not used here) constPointoperator+ (constPoint& lhs, constint& v) { return Point(lhs._x + v, lhs._y + v); } ostream& operator<<( ostream& o, constPoint &p ) { o << "(" << p.x() << "," << p.y() << ")"; return o; } Within Source File (not scoped for class)

  9. Operator overloading • CLASS (use when necessary or more convenient) constPoint& Point::operator= (constPoint& rhs) { this->_x = rhs.x(); this->_y = rhs.y(); return *this; } Within Source File (scoped for class)

  10. Operator overloading • FREE (efficiency issues – must use accessor and mutator functions) constPointoperator- (constPoint& lhs, constPoint& rhs) { return Point(lhs.x() - rhs.x(), lhs.y() - rhs.y()); } Within Source File (not scoped for class)

  11. Const • The five types of const prevent the following from modification: • const variable: the variable (local and global variables) • const argument: the argument • const return type: this only only applied to references to members of a class. Then, const can prevent the original member from being modified. • const method: all non-mutable class members • const member: the member (class member - once object is constructed - this value can’t change)

  12. Const • For parameters to member function: the parameter value can not be changed. • Particularly useful when using the reference qualifier: voidaddCow(const Cow& heifer) {list_ = list_+heifer;} Otherwise - the function would have the ability to change the value of the argument being passed in.

  13. Const • For class usage of a member function - the function can not change the values of any class variables voiddisplayBrands() const;

  14. Const • The value of a return type that is declared const cannot be changed. This is especially useful when giving a reference to a class's internals. struct Values { const std::vector<int>& GetValues() const { return mV; } private: std::vector<int> mV; }; C++ Structure and C++ class are exactly same except default access specifier of their members - in C++ Structure all members are public by default while in Class all are private. NOTE: Use const whenever possible.

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