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>
  5. using namespace std;
  7. int main()
  8. {
  10.         map<int, string> mapStudent;
  12.         mapStudent.insert(pair<int, string>(1, "student_one"));
  13.         mapStudent.insert(pair<int, string>(2, "student_two"));
  14.         mapStudent.insert(pair<int, string>(3, "student_three"));
  16.         map<int, string>::iterator iter;
  18.         for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
  19.                 cout << iter->first << " " << iter->second << endl;
  21. }

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>
  5. using namespace std;
  7. int main()
  8. {
  10.         map<int, string> mapStudent;
  12.         mapStudent.insert(map<int, string>::value_type (1, "student_one"));
  13.         mapStudent.insert(map<int, string>::value_type (2, "student_two"));
  14.         mapStudent.insert(map<int, string>::value_type (3, "student_three"));
  16.         map<int, string>::iterator iter;
  18.         for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
  19.                 cout << iter->first << " " << iter->second << endl;
  21. }

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>
  5. using namespace std;
  7. int main()
  8. {
  10.         map<int, string> mapStudent;
  12.         mapStudent[1] = "student_one";
  13.         mapStudent[2] = "student_two";
  14.         mapStudent[3] = "student_three";
  16.         /* the below will cover the above
  17.         mapStudent[3] = "student_three_1";
  18.         */
  19.         map<int, string>::iterator iter;
  21.         for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
  22.                 cout << iter->first << " " << iter->second << endl;
  24.         cout << "student size:" << mapStudent.size() << endl;
  25. }

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;
  4. int main()
  5. {
  7.         map<int, string> mapStudent;
  9.         #define MAP_INSERT_CHECK(nr,str) do {
  10.                 pair < map <int, string>::iterator,bool> InsertPair;
  11.                 InsertPair = mapStudent.insert(pair<int, string>(nr, str));
  12.                 if(InsertPair.second)
  13.                         cout << "Insert Successfully ";
  14.                 else
  15.                         cout << "Insert Failure " ;
  16.         }while(0)
  18.         MAP_INSERT_CHECK(1,"student_one");
  19.         MAP_INSERT_CHECK(2,"student_two");
  20.         MAP_INSERT_CHECK(3,"student_three");
  22.         map<int, string>::iterator iter;
  24.         for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
  25.                 cout << iter->first << " " << iter->second << endl;
  27.         cout << "student size:" << mapStudent.size() << endl;
  29. }

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>
  5. using namespace std;
  7. int main()
  8. {
  10.         map<int, string> mapStudent;
  12.         mapStudent.insert(pair<int, string>(1, "student_one"));
  13.         mapStudent.insert(pair<int, string>(2, "student_two"));
  14.         mapStudent.insert(pair<int, string>(3, "student_three"));
  16.         int size = mapStudent.size();
  18.         for(int i=0; i<size; i++)
  19.                 cout << i+1 << " " << mapStudent[i+1] << endl;
  21. }

upper_bound，很有意思的东西

  1. #include <map>
  2. #include <string>
  3. #include <iostream>
  5. using namespace std;
  7. int main()
  8. {
  10.         map<int, string> mapStudent;
  12.         mapStudent[1] = "student_one";
  13.         mapStudent[3] = "student_three";
  14.         mapStudent[5] = "student_five";
  16.         map<int, string>::iterator iter;
  17.         for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
  18.                 cout << iter->first << " " << iter->second << endl;
  20.         cout << "student size:" << mapStudent.size() << endl;
  22.         cout << "test bound " ;
  24.         iter = mapStudent.lower_bound(2);
  25.         cout <<"lower_bound(2):" <<iter->second << endl;
  27.         iter = mapStudent.upper_bound(2);
  28.         cout <<"upper_bound(2):" <<iter->second << endl;
  30.         iter = mapStudent.lower_bound(3);
  31.         cout <<"lower_bound(3):" <<iter->second << endl;
  33.         iter = mapStudent.upper_bound(3);
  34.         cout <<"upper_bound(3):" <<iter->second << endl;
  37.         /* for justifying exiting */
  38.         pair < map<int,string>::iterator, map<int,string>::iterator > mapPair;
  39.         mapPair = mapStudent.equal_range(2);
  40.         if(mapPair.first == mapPair.second)
  41.                 cout <<"key 2 not find ";
  42.         else
  43.                 cout <<"key 2 fount ";
  45.         mapPair = mapStudent.equal_range(3);
  46.         if(mapPair.first == mapPair.second)
  47.                 cout <<"key 3 not find ";
  48.         else
  49.                 cout <<"key 3 fount ";
  52. }

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>
  5. using namespace std;
  7. int main()
  8. {
  10.         map<int, string> mapStudent;
  12.         mapStudent.insert(pair<int, string>(1, "student_one"));
  13.         mapStudent.insert(pair<int, string>(2, "student_two"));
  14.         mapStudent.insert(pair<int, string>(3, "student_three"));
  16.         map<int, string>::reverse_iterator riter;
  18.         for(riter = mapStudent.rbegin(); riter != mapStudent.rend(); riter++)
  19.                 cout << riter->first << " " << riter->second << endl;
  21. }

 

 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>
  5. using namespace std;
  7. int main()
  8. {
  9.         map<int, string> mapStudent;
  11.         mapStudent.insert(pair<int, string>(1, "student_one"));
  12.         mapStudent.insert(pair<int, string>(3, "student_two"));
  13.         mapStudent.insert(pair<int, string>(5, "student_three"));
  15.         map<int, string>::iterator iter;
  17.         cout << " the BILL of all student" << endl;
  18.         for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
  19.                 cout << iter->first << " " << iter->second << endl;
  20.         cout << "--------------------------" << endl;
  22.         //by iterator
  23.         iter = mapStudent.find(1);
  24.         mapStudent.erase(iter);
  25.         for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
  26.                 cout << " " << iter->first << " " << iter->second << endl;
  28.         //by key
  29.         mapStudent.insert(pair<int, string>(1, "student_one"));
  30.         cout << " the BILL of all student" << endl;
  31.         for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
  32.                 cout << iter->first << " " << iter->second << endl;
  33.         cout << "--------------------------" << endl;
  35.         int rt = 0;
  36.         rt = mapStudent.erase(1);
  37.         cout << "erase(1):" << rt << endl;
  38.         rt = mapStudent.erase(2);
  39.         cout << "erase(2):" << rt << endl;
  40.         for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
  41.                 cout << " " << iter->first << " " << iter->second << endl;
  43.         //delete a range item
  44.         mapStudent.insert(pair<int, string>(1, "student_one"));
  45.         cout << " the BILL of all student" << endl;
  46.         for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
  47.                 cout << iter->first << " " << iter->second << endl;
  48.         cout << "--------------------------" << endl;
  49.         mapStudent.erase(mapStudent.begin(), mapStudent.end());
  50.         //Removes the elements in the range [first; last).
  51.         for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
  52.                 cout << " " << iter->first << " " << iter->second << endl;
  53. }

 

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;
  9.         /* in map, the sort need "<" for sorting, so this needed */
  10.         bool operator < (tagStudentInfo const& _A) const {
  11.                 if(nID < _A.nID) return true;
  12.                 if(nID == _A.nID) return strName.compare(_A.strName) < 0;
  13.                 return false;
  14.         }
  15. }StudentInfo, *PStudentInfo;
  17. int main()
  18. {
  19.         int nSize;
  21.         map<StudentInfo, int>mapStudent;
  22.         map<StudentInfo, int>::iterator iter;
  23.         StudentInfo studentInfo;
  25.         studentInfo.nID = 1;
  26.         studentInfo.strName = "student_one";
  27.         mapStudent.insert(pair<StudentInfo, int>(studentInfo, 90));
  29.         studentInfo.nID = 2;
  30.         studentInfo.strName = "student_two";
  31.         mapStudent.insert(pair<StudentInfo, int>(studentInfo, 80));
  33.         studentInfo.nID = 3;
  34.         studentInfo.strName = "student_three";
  35.         mapStudent.insert(pair<StudentInfo, int>(studentInfo, 95));
  37.         cout << "ID Name Score ";
  38.         for (iter = mapStudent.begin(); iter != mapStudent.end(); iter++ )
  39.                 cout << iter->first.nID <<" "
  40.                         << iter->first.strName <<" "
  41.                         << iter->second <<endl ;
  42. }

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;
  10. class BySort{
  11.         public:
  12.                 bool operator()
  13.                 (StudentInfo const &_A, StudentInfo const &_B) const
  14.                 {
  15.                         if(_A.nID < _B.nID)
  16.                                 return true;
  17.                         if(_A.nID == _B.nID)
  18.                                 return _A.strName.compare(_B.strName) < 0;
  19.                         return false;
  20.                 }
  21. };
  22. int main()
  23. {
  24.         int nSize;
  26.         map<StudentInfo, int, BySort>mapStudent;
  27.         map<StudentInfo, int>::iterator iter;
  28.         StudentInfo studentInfo;
  30.         studentInfo.nID = 1;
  31.         studentInfo.strName = "student_one";
  32.         mapStudent.insert(pair<StudentInfo, int>(studentInfo, 90));
  34.         studentInfo.nID = 2;
  35.         studentInfo.strName = "student_two";
  36.         mapStudent.insert(pair<StudentInfo, int>(studentInfo, 80));
  38.         studentInfo.nID = 3;
  39.         studentInfo.strName = "student_three";
  40.         mapStudent.insert(pair<StudentInfo, int>(studentInfo, 95));
  42.         cout << "ID Name Score ";
  43.         for (iter = mapStudent.begin(); iter != mapStudent.end(); iter++ )
  44.                 cout << iter->first.nID <<" "
  45.                         << iter->first.strName <<" "
  46.                         << iter->second <<endl ;
  47. }

 

 

参考：

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

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

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原文地址：https://www.cnblogs.com/timssd/p/4781071.html