C++ map

C++ map

Map is an associative container that contains a sorted list of unique key-value pairs. That list is sorted using the comparison function Compare applied to the keys. Search, removal, and insertion operations have logarithmic complexity. Maps are usually implemented as red-black trees

Map 是STL的一个关联容器，它提供一对一（其中第一个可以称为关键字，每个关键字只能在map中出现一次，第二个可能称为该关键字的值）的数据处理能力，由 于这个特性，它完成有可能在我们处理一对一数据的时候，在编程上提供快速通道。这里说下map内部数据的组织，map内部自建一颗红黑树(一种非严格意义 上的平衡二叉树)，这颗树具有对数据自动排序的功能，所以在map内部所有的数据都是有序的，后边我们会见识到有序的好处。

下 面举例说明什么是一对一的数据映射。比如一个班级中，每个学生的学号跟他的姓名就存在着一一映射的关系，这个模型用map可能轻易描述，很明显学号用 int描述，姓名用字符串描述(本篇文章中不用char *来描述字符串，而是采用STL中string来描述),下面给出map描述代码：

Map mapStudent;

1.       map的构造函数

map共提供了6个构造函数，这块涉及到内存分配器这些东西，略过不表，在下面我们将接触到一些map的构造方法，这里要说下的就是，我们通常用如下方法构造一个map：

Map mapStudent;

2.       数据的插入

在构造map容器后，我们就可以往里面插入数据了。这里讲三种插入数据的方法：

第一种：用insert函数插入pair数据，下面举例说明

1. #include <map>
2. #include <string>
3. #include <iostream>
4. using namespace std;
5. int main()
6. {
7. map<int, string> mapStudent;
8. mapStudent.insert(pair<int, string>(1, "student_one"));
9. mapStudent.insert(pair<int, string>(2, "student_two"));
10. mapStudent.insert(pair<int, string>(3, "student_three"));
11. map<int, string>::iterator iter;
12. for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
13. cout << iter->first << " " << iter->second << endl;
14. }

第二种：用insert函数插入value_type数据，下面举例说明

1. #include <map>
2. #include <string>
3. #include <iostream>
4. using namespace std;
5. int main()
6. {
7. map<int, string> mapStudent;
8. mapStudent.insert(map<int, string>::value_type (1, "student_one"));
9. mapStudent.insert(map<int, string>::value_type (2, "student_two"));
10. mapStudent.insert(map<int, string>::value_type (3, "student_three"));
11. map<int, string>::iterator iter;
12. for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
13. cout << iter->first << " " << iter->second << endl;
14. }

第三种：用数组方式插入数据，下面举例说明

1. #include <map>
2. #include <string>
3. #include <iostream>
4. using namespace std;
5. int main()
6. {
7. map<int, string> mapStudent;
8. mapStudent[1] = "student_one";
9. mapStudent[2] = "student_two";
10. mapStudent[3] = "student_three";
11. /* the below will cover the above
12. mapStudent[3] = "student_three_1";
13. */
14. map<int, string>::iterator iter;
15. for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
16. cout << iter->first << " " << iter->second << endl;
17. cout << "student size:" << mapStudent.size() << endl;
18. }

以
上三种用法，虽然都可以实现数据的插入，但是它们是有区别的，当然了第一种和第二种在效果上是完成一样的，用insert函数插入数据，在数据的插入上涉
及到集合的唯一性这个概念，即当map中有这个关键字时，insert操作是插入数据不了的，但是用数组方式就不同了，它可以覆盖以前该关键字对应的值

用pair来获得是否插入成功

1. using namespace std;
2. int main()
3. {
4. map<int, string> mapStudent;
5. #define MAP_INSERT_CHECK(nr,str) do { \
6. pair < map <int, string>::iterator,bool> InsertPair; \
7. InsertPair = mapStudent.insert(pair<int, string>(nr, str)); \
8. if(InsertPair.second) \
9. cout << "Insert Successfully \n"; \
10. else \
11. cout << "Insert Failure \n" ; \
12. }while(0)
13. MAP_INSERT_CHECK(1,"student_one");
14. MAP_INSERT_CHECK(2,"student_two");
15. MAP_INSERT_CHECK(3,"student_three");
16. map<int, string>::iterator iter;
17. for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
18. cout << iter->first << " " << iter->second << endl;
19. cout << "student size:" << mapStudent.size() << endl;
20. }

上面已经有iterator方式的遍历了，看看数组方式遍历

1. #include <map>
2. #include <string>
3. #include <iostream>
4. using namespace std;
5. int main()
6. {
7. map<int, string> mapStudent;
8. mapStudent.insert(pair<int, string>(1, "student_one"));
9. mapStudent.insert(pair<int, string>(2, "student_two"));
10. mapStudent.insert(pair<int, string>(3, "student_three"));
11. int size = mapStudent.size();
12. for(int i=0; i<size; i++)
13. cout << i+1 << " " << mapStudent[i+1] << endl;
14. }

upper_bound，很有意思的东西

1. #include <map>
2. #include <string>
3. #include <iostream>
4. using namespace std;
5. int main()
6. {
7. map<int, string> mapStudent;
8. mapStudent[1] = "student_one";
9. mapStudent[3] = "student_three";
10. mapStudent[5] = "student_five";
11. map<int, string>::iterator iter;
12. for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
13. cout << iter->first << " " << iter->second << endl;
14. cout << "student size:" << mapStudent.size() << endl;
15. cout << "test bound\n" ;
16. iter = mapStudent.lower_bound(2);
17. cout <<"lower_bound(2):" <<iter->second << endl;
18. iter = mapStudent.upper_bound(2);
19. cout <<"upper_bound(2):" <<iter->second << endl;
20. iter = mapStudent.lower_bound(3);
21. cout <<"lower_bound(3):" <<iter->second << endl;
22. iter = mapStudent.upper_bound(3);
23. cout <<"upper_bound(3):" <<iter->second << endl;
24. /* for justifying exiting */
25. pair < map<int,string>::iterator, map<int,string>::iterator > mapPair;
26. mapPair = mapStudent.equal_range(2);
27. if(mapPair.first == mapPair.second)
28. cout <<"key 2 not find\n";
29. else
30. cout <<"key 2 fount\n";
31. mapPair = mapStudent.equal_range(3);
32. if(mapPair.first == mapPair.second)
33. cout <<"key 3 not find\n";
34. else
35. cout <<"key 3 fount\n";
36. }

反向遍历

看清 不是iterator 而是 reverse_iterator，我是看了好久才检查出来的

1. #include <map>
2. #include <string>
3. #include <iostream>
4. using namespace std;
5. int main()
6. {
7. map<int, string> mapStudent;
8. mapStudent.insert(pair<int, string>(1, "student_one"));
9. mapStudent.insert(pair<int, string>(2, "student_two"));
10. mapStudent.insert(pair<int, string>(3, "student_three"));
11. map<int, string>::reverse_iterator riter;
12. for(riter = mapStudent.rbegin(); riter != mapStudent.rend(); riter++)
13. cout << riter->first << " " << riter->second << endl;
14. }

数据的清空与判空

清空map中的数据可以用clear()函数，判定map中是否有数据可以用empty()函数，它返回true则说明是空map

数据的删除

1. #include <map>
2. #include <string>
3. #include <iostream>
4. using namespace std;
5. int main()
6. {
7. map<int, string> mapStudent;
8. mapStudent.insert(pair<int, string>(1, "student_one"));
9. mapStudent.insert(pair<int, string>(3, "student_two"));
10. mapStudent.insert(pair<int, string>(5, "student_three"));
11. map<int, string>::iterator iter;
12. cout << "\nthe BILL of all student" << endl;
13. for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
14. cout << iter->first << " " << iter->second << endl;
15. cout << "--------------------------" << endl;
16. //by iterator
17. iter = mapStudent.find(1);
18. mapStudent.erase(iter);
19. for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
20. cout << "\t" << iter->first << " " << iter->second << endl;
21. //by key
22. mapStudent.insert(pair<int, string>(1, "student_one"));
23. cout << "\nthe BILL of all student" << endl;
24. for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
25. cout << iter->first << " " << iter->second << endl;
26. cout << "--------------------------" << endl;
27. int rt = 0;
28. rt = mapStudent.erase(1);
29. cout << "erase(1):" << rt << endl;
30. rt = mapStudent.erase(2);
31. cout << "erase(2):" << rt << endl;
32. for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
33. cout << "\t" << iter->first << " " << iter->second << endl;
34. //delete a range item
35. mapStudent.insert(pair<int, string>(1, "student_one"));
36. cout << "\nthe BILL of all student" << endl;
37. for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
38. cout << iter->first << " " << iter->second << endl;
39. cout << "--------------------------" << endl;
40. mapStudent.erase(mapStudent.begin(), mapStudent.end());
41. //Removes the elements in the range [first; last).
42. for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
43. cout << "\t" << iter->first << " " << iter->second << endl;
44. }

排序

因为是红黑树存储，本身要有有顺序，因此在构造时就必须明确iterator->first的比较方法，基本数据类型不说了，如果是结构体有两种，一是在结构体或者类重载“<”，二是利用第三个类进行重载“()”进行排序。

1. #include <map>
2. #include <iostream>
3. #include <string>
4. using namespace std;
5. typedef struct tagStudentInfo {
6. int nID;
7. string strName;
8. /* in map, the sort need "<" for sorting, so this needed */
9. bool operator < (tagStudentInfo const& _A) const {
10. if(nID < _A.nID) return true;
11. if(nID == _A.nID) return strName.compare(_A.strName) < 0;
12. return false;
13. }
14. }StudentInfo, *PStudentInfo;
15. int main()
16. {
17. int nSize;
18. map<StudentInfo, int>mapStudent;
19. map<StudentInfo, int>::iterator iter;
20. StudentInfo studentInfo;
21. studentInfo.nID = 1;
22. studentInfo.strName = "student_one";
23. mapStudent.insert(pair<StudentInfo, int>(studentInfo, 90));
24. studentInfo.nID = 2;
25. studentInfo.strName = "student_two";
26. mapStudent.insert(pair<StudentInfo, int>(studentInfo, 80));
27. studentInfo.nID = 3;
28. studentInfo.strName = "student_three";
29. mapStudent.insert(pair<StudentInfo, int>(studentInfo, 95));
30. cout << "ID\tName\t\tScore\n";
31. for (iter = mapStudent.begin(); iter != mapStudent.end(); iter++ )
32. cout << iter->first.nID <<"\t"
33. << iter->first.strName <<"\t"
34. << iter->second <<endl ;
35. }

第二种

1. #include <map>
2. #include <iostream>
3. #include <string>
4. using namespace std;
5. typedef struct tagStudentInfo {
6. int nID;
7. string strName;
8. }StudentInfo, *PStudentInfo;
9. class BySort{
10. public:
11. bool operator()
12. (StudentInfo const &_A, StudentInfo const &_B) const
13. {
14. if(_A.nID < _B.nID)
15. return true;
16. if(_A.nID == _B.nID)
17. return _A.strName.compare(_B.strName) < 0;
18. return false;
19. }
20. };
21. int main()
22. {
23. int nSize;
24. map<StudentInfo, int, BySort>mapStudent;
25. map<StudentInfo, int>::iterator iter;
26. StudentInfo studentInfo;
27. studentInfo.nID = 1;
28. studentInfo.strName = "student_one";
29. mapStudent.insert(pair<StudentInfo, int>(studentInfo, 90));
30. studentInfo.nID = 2;
31. studentInfo.strName = "student_two";
32. mapStudent.insert(pair<StudentInfo, int>(studentInfo, 80));
33. studentInfo.nID = 3;
34. studentInfo.strName = "student_three";
35. mapStudent.insert(pair<StudentInfo, int>(studentInfo, 95));
36. cout << "ID\tName\t\tScore\n";
37. for (iter = mapStudent.begin(); iter != mapStudent.end(); iter++ )
38. cout << iter->first.nID <<"\t"
39. << iter->first.strName <<"\t"
40. << iter->second <<endl ;
41. }

参考：

http://www.cnblogs.com/wanghao111/archive/2009/08/10/1542974.html

http://en.cppreference.com/w/cpp/container/map