作用：实现两个自定义数据类型的相加运算

    示例：

    1. #include<iostream>
    2. using namespace std;
    3. class Building
    4. {
    5.     public:
    6.     int m_age1;
    7.     int m_age2;
    8.     //成员函数重载+号。 
    9. //    成员函数重载本质调用 
    10. //    Building operator+(Building &p)
    11. //    {
    12. //        Building temp;
    13. //        temp.m_age1=this->m_age1+p.m_age1;
    14. //        temp.m_age2=this->m_age2+p.m_age2;
    15. //        return temp;
    16. //    }
    17. };
    19. //全局函数重载+号
    20. Building operator+(Building &p1,Building &p2)
    21. {
    22.     Building temp;
    23.     temp.m_age1=p1.m_age1+p2.m_age1;
    24.     temp.m_age2=p1.m_age2+p2.m_age2;
    25.     return temp;
    26. }
    28. Building operator+(Building &p1,int num)
    29. {
    30.     Building temp;
    31.     temp.m_age1=p1.m_age1+num;
    32.     temp.m_age2=p1.m_age2+num;
    33.     return temp;
    34. }  
    35. void show()
    36. {
    37.     Building p1;
    38.     p1.m_age1=10;
    39.     p1.m_age2=10;
    40.     Building p2;
    41.     p2.m_age1=10;
    42.     p2.m_age2=10;
    43. //    Building p3=p1+p2;
    44.     Building p3;
    45.     Building p4;
    46.     //成员函数重载本质调用
    47. //    p3=p1.operator+(p2);
    48.     //全局函数本质的调用
    49. //    p3=operator+(p1,p2);
    50. //  简化版 
    51.     p3=p1+p2;
    52.     p4=p1+100;//运算符重载也可以发生函数重载。 
    53.     cout<<"p3.age1:"<<p3.m_age1<<endl;
    54.     cout<<"p3.age2:"<<p3.m_age2<<endl;
    55.     cout<<"p4.age1:"<<p4.m_age1<<endl;
    56.     cout<<"p4.age2:"<<p4.m_age2<<endl;
    57. }
    58. int main()
    59. {
    60.     show();
    61.     return 0; 
    62. }

    网址：https://www.bilibili.com/video/BV1et411b73Z?p=121