二元运算符又称为双目运算符,即需要2个操作数的运算符,例如 + - * / 等。
运算符重载可以分为3种方式:类的非静态成员函数、类的友元函数、普通函数。
例如有 2 个操作数 a 和 b,二元运算符 ? (表示一个二元运算符),a ? b 的操作会被解释为下面2种形式之一
//a ? b a.operator?(b); //类的非静态成员函数 operator?(a, b); //友元函数 和 普通函数
第一种形式是运算符被重载为类的非静态成员函数,
这种方式要求运算符左边的的操作数(即第一个操作数a)必须是一个对象,operator?是这个对象的非静态成员函数
并且只能有一个参数。
第二种形式是运算符被重载为类的友元函数 或 普通函数,
这种方式需要2个参数,
重载为 类的友元函数 和 普通函数的区别是 类的友元函数可以直接访问类的私有成员,而普通函数不可以。
下例中有3个complex类 ComplexA、ComplexB 和 ComplexC,3个类都重载了加减乘除 运算符。
其中ComplexA使用类的非静态成员函数方式重载,ComplexB使用类的友元函数方式重载,ComplexC使用普通函数方式重载。
需要注意的是复数的加减乘除运算的算法是有问题的,只是一个说明重载方法的例子,
另外重载函数的参数最好使用const关键字限定,至于返回值是否用const限定,需要取决于你的设计,比如允许C3 = ++(C1+C2)这种情况,就不能用cosnt限定。
至于不同类型的对象间的操作,通常是没有意义的。
#include <iostream> using namespace std; class ComplexA { public: //默认构造函数(Default constructor) ComplexA(){cout<<"Default Constructor"<<endl;} //带参数的构造函数(The constructor with parameters) ComplexA(double re, double im):real(re),image(im){cout<<"Parameter Constructor"<<endl;} //拷贝构造函数(Copy constructor) ComplexA(const ComplexA& ref){real = ref.real; image = ref.image; cout<<"Copy Constructor"<<endl;} //析构函数(destructor) ~ComplexA(){cout<<"Destructor"<<endl;} //Operator Overload : + ComplexA operator+(ComplexA& ref) { return ComplexA(real + ref.real, image + ref.image); } //Operator Overload : - ComplexA operator-(ComplexA& ref) { return ComplexA(real - ref.real, image - ref.image); } //Operator Overload : * ComplexA operator*(ComplexA& ref) { return ComplexA(real * ref.real, image * ref.image); } //Operator Overload : / ComplexA operator/(ComplexA& ref) { return ComplexA(real / ref.real, image / ref.image); } //display void display(void){cout<<real<<"+"<<image<<"i"<<endl;} private: double real; //复数的实部 double image; //复数的虚部 }; class ComplexB { public: //默认构造函数(Default constructor) ComplexB(){cout<<"Default Constructor"<<endl;} //带参数的构造函数(The constructor with parameters) ComplexB(double re, double im):real(re),image(im){cout<<"Parameter Constructor"<<endl;} //拷贝构造函数(Copy constructor) ComplexB(const ComplexB& ref){real = ref.real; image = ref.image; cout<<"Copy Constructor"<<endl;} //析构函数(destructor) ~ComplexB(){cout<<"Destructor"<<endl;} //Operator Overload : + friend ComplexB operator+(ComplexB& ref1, ComplexB& ref2) { return ComplexB(ref1.real + ref2.real, ref1.image + ref2.image); } //Operator Overload : - friend ComplexB operator-(ComplexB& ref1, ComplexB& ref2) { return ComplexB(ref1.real - ref2.real, ref1.image - ref2.image); } //Operator Overload : * friend ComplexB operator*(ComplexB& ref1, ComplexB& ref2) { return ComplexB(ref1.real * ref2.real, ref1.image * ref2.image); } //Operator Overload : / friend ComplexB operator/(ComplexB& ref1, ComplexB& ref2) { return ComplexB(ref1.real / ref2.real, ref1.image / ref2.image); } //display void display(void){cout<<real<<"+"<<image<<"i"<<endl;} private: double real; //复数的实部 double image; //复数的虚部 }; class ComplexC { public: //默认构造函数(Default constructor) ComplexC(){cout<<"Default Constructor"<<endl;} //带参数的构造函数(The constructor with parameters) ComplexC(double re, double im):real(re),image(im){cout<<"Parameter Constructor"<<endl;} //拷贝构造函数(Copy constructor) ComplexC(const ComplexC& ref){real = ref.real; image = ref.image; cout<<"Copy Constructor"<<endl;} //析构函数(destructor) ~ComplexC(){cout<<"Destructor"<<endl;} //Get Data double GetReal(void){return real;} double GetImage(void){return image;}
//display void display(void){cout<<real<<"+"<<image<<"i"<<endl;} private: double real; //复数的实部 double image; //复数的虚部 }; //Operator Overload : + ComplexC operator+(ComplexC& ref1, ComplexC& ref2) { return ComplexC(ref1.GetReal() + ref2.GetReal(), ref1.GetImage() + ref2.GetImage()); } //Operator Overload : - ComplexC operator-(ComplexC& ref1, ComplexC& ref2) { return ComplexC(ref1.GetReal() - ref2.GetReal(), ref1.GetImage() - ref2.GetImage()); } //Operator Overload : * ComplexC operator*(ComplexC& ref1, ComplexC& ref2) { return ComplexC(ref1.GetReal() * ref2.GetReal(), ref1.GetImage() * ref2.GetImage()); } //Operator Overload : / ComplexC operator/(ComplexC& ref1, ComplexC& ref2) { return ComplexC(ref1.GetReal() / ref2.GetReal(), ref1.GetImage() / ref2.GetImage()); } int main(void) { ComplexA C1(2,4), C2(1, 2), C3; C3 = C1 + C2; C3.display(); C3 = C1 - C2; C3.display(); C3 = C1 * C2; C3.display(); C3 = C1 / C2; C3.display(); cout <<"--------------------------------------"<<endl; ComplexB C4(2,4), C5(1, 2), C6; C6 = C4 + C5; C6.display(); C6 = C4 - C5; C6.display(); C6 = C4 * C5; C6.display(); C6 = C4 / C5; C6.display(); cout <<"--------------------------------------"<<endl; ComplexC C7(2,4), C8(1, 2), C9; C9 = C7 + C8; C9.display(); C9 = C7 - C8; C9.display(); C9 = C7 * C8; C9.display(); C9 = C7 / C8; C9.display(); return 0; }
上面的例子中是对象 和 对象之间的运算符重载,如果需要一个是对象 + char/int/float/double,或者反过来 char/int/float/double + 对象,这时上面的程序的重载方式就不适用了。
需要定义新的重载,如下列程序所示。
#include <iostream> using namespace std; class ComplexD { public: ComplexD(double re = 0, double im = 0):real(re),image(im){} ComplexD operator+(ComplexD& ref){return ComplexD(real+ref.real, image+ref.image);}; ComplexD operator+(int a){cout<<"IN\t int \t\t";return ComplexD(real+a, image);}; ComplexD operator+(double d){cout<<"IN\t double \t";return ComplexD(real+d, image);}; ComplexD operator+(float f){cout<<"IN\t float \t\t";return ComplexD(real+f, image);}; void display(void){cout<<real<<"+"<<image<<"i"<<endl;} double GetReal(void){return real;} double GetImage(void){return image;} private: double real; double image; }; ComplexD operator+(int a, ComplexD& ref){cout<<"OUT\t int \t\t";return ComplexD(ref.GetReal()+a, ref.GetImage());}; ComplexD operator+(double d, ComplexD& ref){cout<<"OUT\t double \t";return ComplexD(ref.GetReal()+d, ref.GetImage());}; ComplexD operator+(float f, ComplexD& ref){cout<<"OUT\t float \t\t";return ComplexD(ref.GetReal()+f, ref.GetImage());}; int main(void) { ComplexD D1(2,4), D2; D2 = D1 + 2; D2.display(); D2 = D1 + 2.1f; D2.display(); D2 = D1 + 2.1; D2.display(); D2 = 2 +D1; D2.display(); D2 = 2.1f + D1; D2.display(); D2 = 2.1 +D1; D2.display(); return 0; }
C++运算符重载——重载二元运算符,布布扣,bubuko.com
原文:http://www.cnblogs.com/LubinLew/p/CppOperatorOverload-BinaryOperator.html