• 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
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