Function Overloading

Transcription

1 Function Overloading C++ supports writing more than one function with the same name but different argument lists. This could include: different data types different number of arguments The advantage is that the same apparent function can be called to perform similar but different tasks. The following will show an example of this.

2 Function Overloading void swap (int *a, int *b) ; void swap (float *c, float *d) ; void swap (char *p, char *q) ; int main ( ) { int a = 4, b = 6 ; float c = 16.7, d = ; char p = 'M', q = 'n' ; swap (&a, &b) ; swap (&c, &d) ; swap (&p, &q) ; }

3 Function Overloading void swap (int *a, int *b) { int temp; temp = *a; *a = *b; *b = temp; } void swap (float *c, float *d) { float temp; temp = *c; *c = *d; *d = temp; } void swap (char *p, char *q) { char temp; temp = *p; *p = *q; *q = temp; }

4 Operator Overloading C++ already has a number of types (e.g., int, float, char, etc.) that each have a number of built in operators. For example, a float can be added to another float and stored in yet another float with use of the + and = operators: floatc = floata + floatb; In this statement, floatb is passed to floata by way of the + operator. The + operator from floata then generates another float that is passed to floatc via the = operator. That new float is then stored in floatc by some method outlined in the = function.

5 Operator Overloading Operator overloading means that the operators: Have multiple definitions that are distinguished by the types of their parameters, and When the operator is used, the C++ compiler uses the types of the operands to determine which definition should be used. Operator overloading is a more elegant way of making function calls. Syntactically different from function calls. The parameters do not appear inside parenthesis, but next to operator characters. Everything you do with operator overloading you can do with regular function calls.

6 Operator Overloading A programmer has the ability to re-define or change how the operators (+, -, *, /, =, <<, >>, etc.) work on their own classes. Overloading operators usually consists of defining a class member function called operator+ (where + is any operator). Note that operator is a reserved word in C++. If anything usually follows that operator, it is passed to the function. That function acts exactly like any other member function; it has the same scope as other member functions and can return a value just like any other member function.

7 Operator defined as a friend function class point { public: point (int x = 0, int y = 0); void print(); int x() {return m_x}; int y() {return m_y}; friend point operator+ (point& a, point& b); private: int m_x, m_y; }; point operator+ (point& a, point& b) { point temp; tmp.m_x = a.m_x + b.m_x; tmp.m_y = a.m_y + b.m_y; return tmp;}

8 Operator defined as a member function class point { public: point (int x = 0, int y = 0); void print(); int x() {return m_x}; int y() {return m_y}; point operator+ (point& a); private: int m_x, m_y; }; point point::operator+ (point& a) { point temp; tmp.m_x = a.m_x + m_x; tmp.m_y = a.m_y + m_y; return tmp;}

9 Operator Overloading an example class Complex{ public: Complex(float re, float im ); friend Complex operator+(float first, Complex &second); private: float real, imag; }; Complex operator+( float first, Complex &second) { return Complex(first + second.real, second.imag); }

10 Operator Overloading operator << and >> can be defined only as friend function class Complex {... friend ostream& operator<<(ostream & cout,complex arg); }; ostream& operator<<(ostream & cout, Complex arg) { cout << arg.real<< << arg.img; return cout; }

11 An example #include <iostream.h> class box { int length; int width; public: void set(int l, int w) { lenght = l; width = w; } int computefield (void) {return length * width;} friend box operator+(box a, box b); // Addition friend box operator+(int a, box b); // Widen box friend box operator*(int a, box b); // Increase box };

12 An example box operator+(box a, box b) // Addition { box temp; temp. length = a. length; temp. width = a. width + b. width; return temp; } box operator+(int a, box b) // Widen box { box temp; temp. length = b. length; temp. width = a + b. width; return temp; } box operator*(int a, box b) // Increase box { box temp; temp. length = a * b. length; temp. width = a * b. width; return temp; }

13 An example main() { box small, medium, large; box temp; small.set(2, 4); medium. set((5, 6); large. set(8, 10); cout << Field = " << small. computefield() << "\n"; cout << " Field = " << medium. computefield() << "\n"; cout << " Field = " << large.computefield() << "\n"; temp = male + medium; cout << New field = " << temp. computefield() << "\n"; temp = 10 + male; cout << " New field = " << temp. computefield() << "\n"; temp = 4 * duze; cout << " New field = " << temp. computefield() << "\n"; }