c++中运算符重载

c++语言中运算符重载都是通过函数来实现的，所以其实质为函数重载，当c++语言原有的一个运算符被重载之后，它原来所具有的语义并没有消失，只相当于针对一个特定的类定义了一个新的运算符。

<1>用成员函数重载运算符

例1：

#include <iostream>
using namespace std;
class RMB{
public:
    RMB(unsigned int  d,unsigned int c);
    RMB operator+(RMB&);
    RMB& operator++();
    void display(){
        cout<<(yuan+jf/100.0)<<endl;
    }
protected:
    unsigned int yuan;
    unsigned int jf;
};
RMB::RMB(unsigned int d,unsigned int c){
    yuan=d;
    jf=c;
    while(jf>=100){
        yuan++;
        jf-=100;
    }
}
RMB RMB::operator +(RMB& s){
    unsigned int c=jf+s.jf;
    unsigned int d=yuan+s.yuan;
    RMB result(d,c);
    return result;
}
RMB& RMB::operator++(){
    jf++;
    if(jf>=100){
        jf-=100;
        yuan++;
    }
    return *this;
}
int main(){
    RMB d1(1,60);
    RMB d2(2,50);
    RMB d3(0,0);
    d3=d1+d2;
    ++d3;
    d3.display();
    return 0;
}

结果：4.11

例2：

#include <iostream>
#include <string>
using namespace std;
class String
{
    char name[256];
public:
    String(char* str){
        strcpy(name,str);
    }
    String(){
    }
    ~String(){
    }
    String operator+(const String&);
    void display(){
        cout<<"The string is:"<<name<<endl;
    }
};
static char* str;
String String::operator+(const String& a){
    strcpy(str,name);
    strcat(str,a.name);
    return String(str);//等价于return str；进行自动类型转换
}
int main(){
    str=new char[256];
    String demo1("Visual C++");
    String demo2("6.0");
    demo1.display();
    demo2.display();
    String demo3=demo1+demo2;
    demo3.display();
    String demo4=demo3+"Programming .";
    demo4.display();
    delete str;
    return 0;
}

结果：

例3:

#include <iostream>
#include <string>
using namespace std;
class String
{
    char name[256];
public:
    String(char* str){
        cout<<"constructor,char*--->String\n";
        strcpy(name,str);
    }
    String(String &s){
        cout<<"copy constructor\n";
        strcpy(name,s.name);
    }
    String(){
        cout<<"default constructor\n";
    }
    ~String(){
    }
    void operator=(const String&s){
        strcpy(name,s.name);
        cout<<"operator ="<<endl;
    }
    String operator+(const String&);
    void display(){
        cout<<"The string is:"<<name<<endl;
    }
};
static char* str;
String String::operator+(const String& a){
    String s;
    cout<<"operator +\n";
    strcpy(s.name,name);
    strcat(s.name,a.name);
//    return String(str);//等价于return str；进行自动类型转换
    return s;
}
int main(){
    str=new char[256];
    String demo1("Visual C++");
    String demo2("6.0");
    demo1.display();
    demo2.display();
    String demo3;
    demo3=demo1+demo2;
    cout<<"---------------\n";
    demo3.display();
    String demo4;
    demo4=demo3+"Programming .";
    demo4.display();
    delete str;
    cout<<"---------------\n";
    String demo5=demo4;
    demo5.display();
    return 0;
}

结果：

ps:注意拷贝构造函数的应用!23333

<2>友元函数重载运算符