Microsoft PowerPoint - 8. 运算符重载 Operator Overloading.pptx

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鹿养乐
5 years ago
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1 运算符重载 Operator Overloading

2 class Point { public: ; double x_, y_; Why Operator Overloading? Point (double x =0, double y = 0):x_(x),y_(y) { int main(){ Point a(1., 2), b(3,4); Point c = a + b; return 0;

3 class Point { public: ; double x_, y_; Why Operator Overloading? Point (double x =0, double y = 0):x_(x),y_(y) { int main(){ Point a(1., 2), b(3,4); Point c = a + b; return 0; error: no match for 'operator+' (operand types are 'Point' and 'Point') Point c = a + b;

4 可重载的运算符 What Can I Overload? Algorithm +, -, *, /, %, ^, &,, ~,!, =, +=, -=, *=, /=, %=, ^=, &=, =, &&,, ++, --, Comparison!=, ==, <, <=, >, >= Access [ ], *,->, ( ), Stream <<, >>, >>=, <<= Scary New, delete, New[], delete[],,

5 Operator Overloading 允许我们对新类型重新定义 == 等运算符的新含义. 当且仅当两点的 x, y 坐标分别相等. 如何重载一个运算符? 两种方式 : Member function syntax Free function syntax

6 Operator Overloading 允许我们对新类型重新定义 == 等运算符的新含义 class Point { public: double x_, y_; Point (double x =0, double y = 0):x_(x),y_(y) { bool operator== (const Point& rhs){ return (x == rhs.x && y == rhs.y); ;

7 int main(){ Point p1(3, 2); Point p2(3, 2); if (p1 == p2) cout << Points are equal! << endl; return 0;

8 int main(){ Point p1(3, 2); Point p2(3, 2); if (p1. operator== p2) cout << Points are equal! << endl; return 0;

9 Free Function Syntax bool operator==(point l, Point r) { return l.x == r.x && l.y == r.y; int main(){ Point p1(3, 2); Point p2(3, 2); if (p1 == p2) cout << Points are equal! << endl; return 0;

10 Free Function Syntax Point operator*(double l, Point r) { Point result(l * r.x, l * r.y); return result; int main(){ Point p(1, 1); Point result = 5 * p; result.print(); // prints (5, 5) return 0;

11 Free Function Syntax bool operator==(point l, Point r) { return l.x == r.x && l.y == r.y; int main(){ Point p1(3, 2); Point p2(3, 2); if (operator== (p1, p2) ) cout << Points are equal! << endl; return 0;

12 class Point { public: ; double x_, y_; Operator Overloading Point (double x =0, double y = 0):x_(x),y_(y) { Point operator+ (Point Q){ return Point( x_+ Q.x_, y_+ Q.y_);

13 class Point { public: ; double x_, y_; Operator Overloading Point (double x =0, double y = 0):x_(x),y_(y) { Point operator+ (Point P, Point Q){ return Point( P.x_+ Q.x_, P.y_+ Q.y_);

14 可解释为 aa.operator@(bb), 或 operator@(aa,bb) 可以定义为取一个参数的非静态成员函数, 也可以定义为两个参数的非成员函数当左操作数不是类类型时, 则必须为非成员函数 class X{ ; public: void operator+(int); X(int); void operator=(x,x); void operator=(x,double); void f(x a){ a+2; 2.operator+(a); a+2.5

15 可解释为 aa.operator@(), 或 operator@(aa)

16 ++i vs i++ int i = 1; // i = 1 int j = i++; // j = 1, i = 2 int k = ++i; // k = 3, i = 3

17 class foo { // Define ++foo foo operator++() { // Define foo++ foo operator++(int) { ++i vs i++ int i = 1; // i = 1 int j = i++; // j = 1, i = 2 int k = ++i; // k = 3, i = 3

18 Cautions: 运算符定义不能违背约定的语法如不能将一元运算符定义为二元的或三元的 class X { ; X* operator&() ; // 一元取地址 X operator&(x) ; // 二元与 X operator++(int) ; // 后缀增量 X operator&(x,x) ; // error: ternary X operator/() ; // error: unary /

19 Cautions: 运算符定义不能违背约定的语法 // nonmember functions : X operator-(x) ; // prefix unary minus X operator-(x,x) ; // binary minus X operator--(x&,int) ; // postfix decrement X operator-(); // error: no operand X operator-(x,x,x) ; // error: ternary X operator%(x) ; // error: unary %

20 Other Cautions 其他注意点重载运算符不能有缺省参数除 operator= 外, 重载运算符被派生类所继承重载运算符的第一个参数一定是该类或派生类类型如 point p; 3.+=p; // 错!

21 Other Cautions 其他注意点 = [] () -> 必须是非静态成员函数为防止误用运算符 ( 如 =, &,,), 可以通过定义私有运算符函数, 将它们设为私有 class X { private: ; void operator=(const X&) ; void operator&() ; void operator, (const X&) ; //... void f(x a, X b){ a = b; &a; a, b;

22 赋值运算符 = 下标运算符 [] 类成员访问运算符 -> 类型转换运算符 T() 函数调用运算符 () 几种特殊运算符增量与减量运算符 ++,--

23 赋值运算符 = class String{ char *s; int sz; public: String() {s = 0; sz = 0; String( const char *str); ; String::String(const char *str){ sz = strlen(str); s= new char[sz+1]; strcpy(s,str); void f(){ String s1 = Li,s2; s2 = s1; 拷贝构造函数赋值运算符

24 赋值运算符 = class String{ char *s; int sz; public: ; String() {s = 0; sz = 0; String( const char *str); String& operator= (String &T); String & String::operator= (String &T){ sz = strlen(t.s); s= new char[sz+1]; strcpy(s,t.s); 拷贝构造函数 void f(){ String s1 = Li,s2; s2 = s1; 赋值运算符

25 赋值运算符 = 拷贝构造函数与赋值运算符的区别 : 拷贝构造函数在定义一个对象时被调用, 而赋值运算符用一个对象对另一个对象赋值 class X { X(int); ; void f() { X x, y; X z = x; // 拷贝构造 y = z; // 赋值运算符 x = 3; // 类型转换 + 赋值运算符

26 下标运算符 [] class String{ char *s; int sz; public: // char& operator[](int i){ return s[i]; ; void f(){ String s1 = Li, s2; S1[1] = L ; S1[3] = T ;

27 类成员访问运算符 -> 二元运算符, 其第一操作数是指向类类型的指针. 其第二个操作数是该类的成员 class String{ char *s; int sz; public: // int size(){return sz; ; Void f(){ String s = Li,*p; int n = s.size(); p = &s; n = p->size();

28 类型转换运算符 T() 带参数的构造函数相当于从参数类型到该类类型的类型转换 String(const char *str); 类也可以定义类型转换运算符将该类对象转换为其他类型的对象如 class A{ ; operator int(){;

29 类型转换运算符 T() 当一个类同时定义了一个参数 (t 类型 ) 的构造函数和一个 t 类型的类型转换函数时, 有时会引起歧义 class A{ A( int ); operator int(); friend A operator+ (const A& a1,const A& a2); ; A a; int i = 1,z; z= a+i; //bad z = (int)a +i; 或 z= a +(A)i

30 函数调用运算符 () 函数调用 () 使得类对象可以当场一个函数来使用如 class Matrix{ double operator()( int i, int j ); //double get( int i, int j); ; Matrix M; double s = M(1,2) ; double s = M.get(1,2);

31 友元 friend Complex 类 class complex{ / / very simplified complex double re, im; public: complex(double r, double i) : re(r), im(i) { friend complex operator+ (const complex &a, const complex &b) ; friend complex operator* (const complex &a, const complex &b) ; // ; 类的友元函数可以访问该类对象的私有数据

32 友元 friend Complex 类 complex operator+ (const complex &a, const complex &b) { return Complex( a.re + b.re, a.im + b.im ) ; ; 类的友元函数可以访问该类对象的私有数据

33 作业实现相对完整的 Complex String Matrix 类

Microsoft PowerPoint - string_kruse [兼容模式]

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