在c++中，聚合是一个进程，一个类将另一个类定义为实体引用(一个类作为另一个类的成员)。 这是另一种重用类的方法。 它是一种表示has-a关系的关联形式。

c++聚合示例

下面来看看一个聚合的例子，其中employee类有address类的引用作为数据成员。 这样，它可以重用address类的成员。

#include <iostream>  
using namespace std;  
class address {  
    public:  
   string addressline, city, state;    
     address(string addressline, string city, string state)    
    {    
        this->addressline = addressline;    
        this->city = city;    
        this->state = state;    
    }    
};  
class employee    
    {    
        private:  
        address* address;  //employee has-a address   
        public:  
        int id;    
        string name;    
        employee(int id, string name, address* address)    
       {    
           this->id = id;    
           this->name = name;    
           this->address = address;    
       }    
     void display()    
       {    
           cout<<id <<" "<<name<< " "<<     
             address->addressline<< " "<< address->city<< " "<<address->state<<endl;    
       }    
   };   
int main(void) {  
    address a1= address("renmin road-15","haikou","up");    
    employee e1 = employee(101,"beijing",&a1);    
            e1.display();   
   return 0;  
}

执行上面代码，得到以下结果 -

101 beijing renmin road-15 haikou up