DP書上給出的定義：將對象組合成樹形結構以表示“部分-整體”的層次結構。組合使得用戶對單個對象和組合對象的使用具有一致性。註意兩個字“樹形”。這種樹形結構在現實生活中隨處可見，比如一個集團公司，它有一個母公司，下設很多家子公司。不管是母公司還是子公司，都有各自直屬的財務部、人力資源部、銷售部等。對於母公司來說，不論是子公司，還是直屬的財務部、人力資源部，都是它的部門。整個公司的部門拓撲圖就是一個樹形結構。

下面給出組合模式的UML圖。從圖中可以看到，FinanceDepartment、HRDepartment兩個類作為葉結點，因此沒有定義添加函數。而ConcreteCompany類可以作為中間結點，所以可以有添加函數。那麽怎麽添加呢？這個類中定義了一個鏈表，用來放添加的元素。

  1 // Composite.cpp : 定義控制臺應用程序的入口點。
  2 //
  3 
  4 #include "stdafx.h"
  5 #include<iostream>
  6 #include<string>
  7 #include <vector>
  8 #include <list>
  9 using namespace std;
 10 
 11 class Company
 12 {
 13 public:
 14     Company(string name)
 15     {
 16         m_name = name;
 
 17     }
 18     virtual ~Company() {}
 19     virtual void Add(Company *pCom) {}
 20     virtual void Show(int depth) {}
 21 protected:
 22     string m_name;
 23 };
 24 
 25 class ConcreteCompany : public Company 
 26 {
 27 public:
 28     ConcreteCompany(string name):Company(name) {}
 29     virtual
 
 ~ConcreteCompany() {}
 30     void Add(Company *pCom) {m_listCompany.push_back(pCom);}
 31 
 32     void Show(int depth)
 33     {
 34         for(int i = 0;i < depth; i++)
 35             cout<<"-";
 36         cout<<m_name<<endl;
 37         list<Company *>::iterator iter=m_listCompany.begin();
 38         for(; iter != m_listCompany.end(); iter++) //顯示下層結點
 39             (*iter)->Show(depth + 2);
 40     }
 41 private:
 42     list<Company*> m_listCompany;
 43 
 44 };
 45 
 46 //具體的部門，財務部
 47 
 48 class FinanceDepartment : public Company 
 49 {
 50 public:
 51     FinanceDepartment(string name):Company(name){}
 52     virtual ~FinanceDepartment() {}
 53     virtual void Show(int depth) //只需顯示，無限添加函數，因為已是葉結點
 54     {
 55         for(int i = 0; i < depth; i++)
 56             cout<<"-";
 57         cout<<m_name<<endl;
 58     }
 59 };
 60 
 61 class HRDepartment:public Company
 62 {
 63 public:
 64     HRDepartment(string name):Company(name){}
 65     virtual ~HRDepartment() {}
 66     virtual void Show(int depth)
 67     {
 68         for(int i = 0; i < depth; i++)
 69             cout<<"-";
 70         cout<<m_name<<endl;
 71     }
 72 };
 73 
 74 int _tmain(int argc, _TCHAR* argv[])
 75 {
 76      Company *root = new ConcreteCompany("總公司");
 77      Company *leaf1=new FinanceDepartment("財務部");
 78      Company *leaf2=new HRDepartment("人力資源部");
 79      root->Add(leaf1);
 80      root->Add(leaf2);
 81      //分公司A
 82      Company *mid1 = new ConcreteCompany("分公司A");
 83      Company *leaf3=new FinanceDepartment("財務部");
 84      Company *leaf4=new HRDepartment("人力資源部");
 85      mid1->Add(leaf3);
 86      mid1->Add(leaf4);
 87      root->Add(mid1);
 88 
 89      //分公司B
 90      Company *mid2=new ConcreteCompany("分公司B");
 91      FinanceDepartment *leaf5=new FinanceDepartment("財務部");
 92      HRDepartment *leaf6=new HRDepartment("人力資源部");
 93      mid2->Add(leaf5);
 94      mid2->Add(leaf6);
 95      root->Add(mid2);
 96      root->Show(0);
 97 
 98      delete leaf1; delete leaf2;
 99      delete leaf3; delete leaf4;
100      delete leaf5; delete leaf6;    
101      delete mid1; delete mid2;
102      delete root;
103     system("pause");
104     return 0;
105 }

C++設計模式之組合模式