STL中sort排序算法第三个参数_Compare的实现本质

  1 //本程序为sort排序实现，方法一：重载运算符 方法二：全局的比较函数 方法三：函数对象
  2 //参考http://blog.csdn.net/aastoneaa/article/details/8471722
  3 
  4 //我认为从实现方式看，重载运算符和函数对象实现本质上是一样的：两者都是括号运算符的重载；
  5 //重载运算符利用了泛型模板，再重载模板中的括号运算福，接着重载里面的大于小于操作符；
  6 //而函数对象则是直接针对自己的对象重载括号运算符。
  7 
  8 #include <iostream>
  9 #include <vector>
 10 #include <algorithm>
 11 
 12 using namespace std;
 13 
 14 
 15 //重载运算符
 16 struct TItem
 17 {
 18     int m_i32Type;
 19     int m_i32ID;
 20 
 21     bool operator <(const TItem& rhs) const // 升序排序时必须写的函数
 22     {
 23         return m_i32Type < rhs.m_i32Type;
 24     }
 25     bool operator >(const TItem& rhs) const // 降序排序时必须写的函数
 26     {
 27         return m_i32Type > rhs.m_i32Type;
 28     }
 29 };
 30 int main()
 31 {
 32     vector<TItem> stItemVec;
 33 
 34 
 35     TItem stItem1;
 36     stItem1.m_i32Type = 1;
 37     stItem1.m_i32ID = 1;
 38 
 39     TItem stItem2;
 40     stItem2.m_i32Type = 2;
 41     stItem2.m_i32ID = 2;
 42 
 43     TItem stItem3;
 44     stItem3.m_i32Type = 3;
 45     stItem3.m_i32ID = 3;
 46 
 47     TItem stItem4;
 48     stItem4.m_i32Type = 2;
 49     stItem4.m_i32ID = 4;
 50 
 51     stItemVec.push_back(stItem1);
 52     stItemVec.push_back(stItem2);
 53     stItemVec.push_back(stItem3);
 54     stItemVec.push_back(stItem4);
 55 
 56     // 升序排序
 57     sort(stItemVec.begin(), stItemVec.end(), less<TItem>());
 58     // 或者sort(ctn.begin(), ctn.end());   默认情况为升序
 59 
 60     for (size_t i = 0; i < stItemVec.size(); i++)
 61         printf("type: %d, id: %d\n", stItemVec[i].m_i32Type, stItemVec[i].m_i32ID);
 62 
 63     printf("--\n");
 64 
 65     // 降序排序
 66     sort(stItemVec.begin(), stItemVec.end(), greater<TItem>());
 67 
 68     for (size_t i = 0; i < stItemVec.size(); i++)
 69         printf("type: %d, id: %d\n", stItemVec[i].m_i32Type, stItemVec[i].m_i32ID);
 70 
 71     return 0;
 72 }
 73 
 74 
 75 #if 0
 76 //全局比较函数
 77 struct TItem
 78  {
 79      int m_i32Type;
 80      int m_i32ID;
 81  };
 82 
 83 
 84 bool lessmark(const TItem& stItem1, const TItem& stItem2)
 85  {
 86      return stItem1.m_i32Type < stItem2.m_i32Type;//这里是按照关键字m_i32Type排序，也可以按照关键字m_i32ID排序
 87  }
 88 
 89 
 90 bool greatermark(const TItem& stItem1, const TItem& stItem2)
 91  {
 92      return stItem1.m_i32Type > stItem2.m_i32Type;//这里是按照关键字m_i32Type排序，也可以按照关键字m_i32ID排序
 93  }
 94 
 95 
 96 int main()
 97  {
 98      vector<TItem> stItemVec;
 99 
100 
101     TItem stItem1;
102      stItem1.m_i32Type = 1;
103      stItem1.m_i32ID = 1;
104 
105 
106     TItem stItem2;
107      stItem2.m_i32Type = 2;
108      stItem2.m_i32ID = 2;
109 
110 
111     TItem stItem3;
112      stItem3.m_i32Type = 3;
113      stItem3.m_i32ID = 3;
114 
115 
116     TItem stItem4;
117      stItem4.m_i32Type = 2;
118      stItem4.m_i32ID = 4;
119 
120 
121     stItemVec.push_back(stItem1);
122      stItemVec.push_back(stItem2);
123      stItemVec.push_back(stItem3);
124      stItemVec.push_back(stItem4);
125 
126 
127     sort(stItemVec.begin(), stItemVec.end(), lessmark); //升序排序
128 
129 
130     for (size_t i = 0; i < stItemVec.size(); i++)
131          printf("type: %d, id: %d\n", stItemVec[i].m_i32Type, stItemVec[i].m_i32ID);
132 
133 
134     printf("--\n");
135 
136 
137     sort(stItemVec.begin(), stItemVec.end(), greatermark); //降序排序
138 
139 
140     for (size_t i = 0; i < stItemVec.size(); i++)
141          printf("type: %d, id: %d\n", stItemVec[i].m_i32Type, stItemVec[i].m_i32ID);
142 
143 
144     return 0;
145  }
146 #endif
147 
148 #if 0
149 //函数对象
150 struct TItem
151  {
152      int m_i32Type;
153      int m_i32ID;
154  };
155 
156 
157 class CompLess
158  {
159  public:
160      bool operator ()(const TItem& stItem1, const TItem& stItem2)   //本质上是括号运算符的重载
161      {
162          return stItem1.m_i32Type < stItem2.m_i32Type;
163      }
164  };
165 
166 
167 class CompGreater
168  {
169  public:
170      bool operator ()(const TItem& stItem1, const TItem& stItem2)
171      {
172          return stItem1.m_i32Type > stItem2.m_i32Type;
173      }
174  };
175 
176 
177 int main()
178  {
179      vector<TItem> stItemVec;
180 
181 
182     TItem stItem1;
183      stItem1.m_i32Type = 1;
184      stItem1.m_i32ID = 1;
185 
186 
187     TItem stItem2;
188      stItem2.m_i32Type = 2;
189      stItem2.m_i32ID = 2;
190 
191 
192     TItem stItem3;
193      stItem3.m_i32Type = 3;
194      stItem3.m_i32ID = 3;
195 
196 
197     TItem stItem4;
198      stItem4.m_i32Type = 2;
199      stItem4.m_i32ID = 4;
200 
201 
202     stItemVec.push_back(stItem1);
203      stItemVec.push_back(stItem2);
204      stItemVec.push_back(stItem3);
205      stItemVec.push_back(stItem4);
206 
207 
208     sort(stItemVec.begin(), stItemVec.end(), CompLess()); //升序排序
209 
210 
211     for (size_t i = 0; i < stItemVec.size(); i++)
212          printf("type: %d, id: %d\n", stItemVec[i].m_i32Type, stItemVec[i].m_i32ID);
213 
214 
215     printf("--\n");
216 
217 
218     sort(stItemVec.begin(), stItemVec.end(), CompGreater()); //降序排序
219 
220 
221     for (size_t i = 0; i < stItemVec.size(); i++)
222          printf("type: %d, id: %d\n", stItemVec[i].m_i32Type, stItemVec[i].m_i32ID);
223 
224     return 0;
225  }
226 #endif