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一、运算符重载机制：
一元运算符： @obj => operator @(obj)
二元运算符： obj@obj2 => operator @(obj,obj2)
注意：前置++、--与一元运算符处理方式相同，而后置++、--这样处理：obj++ => operator ++(obj,0)
二、除了.、.*、::、?:、sizeof这5个运算符之外，其他一概都可以重载。
三、普通运算符重载：
1.重载为类的友元函数：
1 #include <iostream> 2 using namespace std; 3 4 class Complex 5 { 6 private: 7 double real; 8 double image; 9 public: 10 Complex(double real=0,double image=0){ this->real=real,this->image=image; } 11 void display(){ cout<<"("<<real<<","<<image<<")"<<endl; } 12 friend Complex operator + (Complex A,Complex B){ return Complex(A.real+B.real,A.image+B.image); }//加法 13 friend Complex operator - (Complex A,Complex B);//减号 14 friend Complex operator - (Complex A);//负号 15 friend Complex operator ++ (Complex& A);//前置++ 16 friend Complex operator ++ (Complex& A,int);//后置++ 17 }; 18 Complex operator - (Complex A,Complex B) { return Complex(A.real-B.real,A.image-B.image); } 19 Complex operator - (Complex A) { return Complex(-A.real,-A.image); } 20 Complex operator ++(Complex& A) { return Complex(++A.real,A.image); } 21 Complex operator ++(Complex& A,int) { return Complex(A.real++,A.image); } 22 23 int main() 24 { 25 Complex A(100.0,200.0),B(-10.0,20.0),C; 26 cout<<"A=";A.display(); 27 cout<<"B=";B.display(); 28 C=A+B; 29 cout<<"C=A+B=";C.display(); 30 C=A-B; 31 cout<<"C=A-B=";C.display(); 32 C=-A+B; 33 cout<<"C=-A+B=";C.display(); 34 C=A++; 35 cout<<"C=A++,C=";C.display(); 36 C=++A; 37 cout<<"C=++A,C=";C.display(); 38 C=A+5; 39 cout<<"C=A+5=";C.display(); 40 return 0; 41 }
2.重载为类的成员函数：
1 #include <iostream> 2 using namespace std; 3 4 class Complex 5 { 6 private: 7 double real; 8 double image; 9 public: 10 Complex(double real=0,double image=0){ this->real=real,this->image=image; } 11 void display(){ cout<<"("<<real<<","<<image<<")"<<endl; } 12 Complex operator + (Complex B);//加法 13 Complex operator - (Complex B);//减号 14 Complex operator - ();//负号 15 Complex operator ++ ();//前置++ 16 Complex operator ++ (int);//后置++ 17 }; 18 Complex Complex::operator +(Complex B) { return Complex(real+B.real,image+B.image); } 19 Complex Complex::operator - (Complex B) { return Complex(real-B.real,image-B.image); } 20 Complex Complex::operator - () { return Complex(-real,-image); } 21 Complex Complex::operator ++() { return Complex(++real,image); } 22 Complex Complex::operator ++(int) { return Complex(real++,image); } 23 24 int main() 25 { 26 Complex A(100.0,200.0),B(-10.0,20.0),C; 27 cout<<"A=";A.display(); 28 cout<<"B=";B.display(); 29 C=A+B; 30 cout<<"C=A+B=";C.display(); 31 C=A-B; 32 cout<<"C=A-B=";C.display(); 33 C=-A+B; 34 cout<<"C=-A+B=";C.display(); 35 C=A++; 36 cout<<"C=A++,C=";C.display(); 37 C=++A; 38 cout<<"C=++A,C=";C.display(); 39 C=A+5; 40 cout<<"C=A+5=";C.display(); 41 return 0; 42 }
3.两种重载方式的比较：
1）一般情况下，单目运算符最好重载为类的成员函数；双目运算符则最好重载为类的友元函数。
2）一些双目运算符不能重载为类的友元函数：=、()、[]、->。
3）若一个运算符的操作需要改变对象的状态，选择重载为成员函数较好。
4）若运算符所需的操作数（尤其第一个操作数）希望有隐式类型转换，则只能选用友元函数。
5）当运算符函数是一个成员函数时，最左边的操作数必须是运算符类的一个类对象或其引用。若左边的操作数必须是一个不同类的对象，或者是一个基本数据类型的对象，该运算符函数必须作为一个友元函数来实现。
6）当需要重载运算符的运算具有可交换性时，选择重载为友元函数。
四、典型运算符重载：
1.重载=进行复数类数据赋值：
1 #include <iostream> 2 using namespace std; 3 4 class Complex 5 { 6 private: 7 double real; 8 double image; 9 public: 10 Complex(double real=0,double image=0) { this->real=real,this->image=image; } 11 void display() { cout<<"("<<real<<","<<image<<")"<<endl; } 12 Complex operator + (Complex B); 13 Complex operator = (Complex B); 14 }; 15 Complex Complex::operator +(Complex B) { return Complex(real+B.real,image+B.image); } 16 Complex Complex::operator =(Complex B) 17 { 18 real=B.real,image=B.image; 19 cout<<"operator = calling..."<<endl; 20 return *this; 21 } 22 int main() 23 { 24 Complex A(100.0,200.0),B(-10.0,20.0),C; 25 cout<<"A=",A.display(); 26 cout<<"B=",B.display(); 27 C=A+B; 28 cout<<"C=A+B=",C.display(); 29 C=A; 30 cout<<"C=A=",C.display(); 31 }
2.->：
1 #include <iostream> 2 using namespace std; 3 4 class Complex 5 { 6 private: 7 double real; 8 double image; 9 public: 10 Complex(double real=0,double image=0) { this->real=real,this->image=image; } 11 void display() { cout<<"("<<real<<","<<image<<")"<<endl; } 12 }; 13 class PComplex 14 { 15 private: 16 Complex *PC; 17 public: 18 PComplex(Complex *PC=NULL) { this->PC=PC; } 19 Complex * operator ->() 20 { 21 static Complex NullComplex(0.0); 22 if(PC==NULL) return &NullComplex; 23 return PC; 24 } 25 }; 26 int main() 27 { 28 PComplex P1; 29 P1->display(); 30 Complex C1(100,200); 31 P1=&C1; 32 P1->display(); 33 return 0; 34 }
3.[]：
1 #include <iostream> 2 #include <cstring> 3 using namespace std; 4 5 class String 6 { 7 private: 8 char *str; 9 int len; 10 public: 11 void showstr() { cout<<"string:"<<str<<",length:"<<len<<endl; } 12 String(const char *p=NULL) 13 { 14 if(p) 15 { 16 len=strlen(p); 17 str=new char[len+1]; 18 strcpy(str,p); 19 } 20 else 21 { 22 len=0; 23 str=NULL; 24 } 25 } 26 ~String() 27 { 28 if(str!=NULL) delete []str; 29 } 30 char &operator[](int n) { return *(str+n); } 31 const char &operator[](int n)const { return *(str+n); } 32 }; 33 34 int main() 35 { 36 String S1("0123456789abcdef"); 37 S1.showstr(); 38 S1[10]=‘A‘; 39 cout<<"S1[10]=A"<<endl; 40 S1.showstr(); 41 const String S2("ABCDEFGHIJKLMN"); 42 cout<<"S2[10]="<<S2[10]<<endl; 43 return 0; 44 }
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原文地址：http://www.cnblogs.com/jiu0821/p/4199824.html
