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

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

#include <map>
#include <string>
#include <iostream>

using namespace std;

int main()
{

        map<int, string> mapStudent;

        mapStudent.insert(pair<int, string>(1, "student_one"));
        mapStudent.insert(pair<int, string>(2, "student_two"));
        mapStudent.insert(pair<int, string>(3, "student_three"));

        map<int, string>::iterator iter;

        for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
                cout << iter->first << " " << iter->second << endl;

}

第二种：用insert函数插入value_type数据，下面举例说明

#include <map>
#include <string>
#include <iostream>

using namespace std;

int main()
{

        map<int, string> mapStudent;

        mapStudent.insert(map<int, string>::value_type (1, "student_one"));
        mapStudent.insert(map<int, string>::value_type (2, "student_two"));
        mapStudent.insert(map<int, string>::value_type (3, "student_three"));

        map<int, string>::iterator iter;

        for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
                cout << iter->first << " " << iter->second << endl;

}

第三种：用数组方式插入数据，下面举例说明

#include <map>
#include <string>
#include <iostream>

using namespace std;

int main()
{

        map<int, string> mapStudent;

        mapStudent[1] = "student_one";
        mapStudent[2] = "student_two";
        mapStudent[3] = "student_three";

        /* the below will cover the above
        mapStudent[3] = "student_three_1";
        */
        map<int, string>::iterator iter;

        for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
                cout << iter->first << " " << iter->second << endl;

        cout << "student size:" << mapStudent.size() << endl;
}

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

using namespace std;


int main()
{

        map<int, string> mapStudent;

        #define MAP_INSERT_CHECK(nr,str) do {                                   \
                pair < map <int, string>::iterator,bool> InsertPair;            \
                InsertPair = mapStudent.insert(pair<int, string>(nr, str));     \
                if(InsertPair.second)                                           \
                        cout << "Insert Successfully \n";                       \
                else                                                            \
                        cout << "Insert Failure \n" ;                           \
        }while(0)

        MAP_INSERT_CHECK(1,"student_one");
        MAP_INSERT_CHECK(2,"student_two");
        MAP_INSERT_CHECK(3,"student_three");

        map<int, string>::iterator iter;

        for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
                cout << iter->first << " " << iter->second << endl;

        cout << "student size:" << mapStudent.size() << endl;

}

上面已经有iterator方式的遍历了，看看数组方式遍历

#include <map>
#include <string>
#include <iostream>

using namespace std;

int main()
{

        map<int, string> mapStudent;

        mapStudent.insert(pair<int, string>(1, "student_one"));
        mapStudent.insert(pair<int, string>(2, "student_two"));
        mapStudent.insert(pair<int, string>(3, "student_three"));

        int size = mapStudent.size();

        for(int i=0; i<size; i++)
                cout << i+1 << " " << mapStudent[i+1] << endl;

}

upper_bound，很有意思的东西

#include <map>
#include <string>
#include <iostream>

using namespace std;

int main()
{

        map<int, string> mapStudent;

        mapStudent[1] = "student_one";
        mapStudent[3] = "student_three";
        mapStudent[5] = "student_five";

        map<int, string>::iterator iter;
        for(iter = mapStudent.begin(); iter != mapStudent.end(); iter++)
                cout << iter->first << " " << iter->second << endl;

        cout << "student size:" << mapStudent.size() << endl;

        cout << "test bound\n" ;

        iter = mapStudent.lower_bound(2);
        cout <<"lower_bound(2):" <<iter->second << endl;

        iter = mapStudent.upper_bound(2);
        cout <<"upper_bound(2):" <<iter->second << endl;

        iter = mapStudent.lower_bound(3);
        cout <<"lower_bound(3):" <<iter->second << endl;

        iter = mapStudent.upper_bound(3);
        cout <<"upper_bound(3):" <<iter->second << endl;


        /* for justifying exiting */
        pair < map<int,string>::iterator, map<int,string>::iterator > mapPair;
        mapPair = mapStudent.equal_range(2);
        if(mapPair.first == mapPair.second)
                cout <<"key 2 not find\n";
        else
                cout <<"key 2 fount\n";

        mapPair = mapStudent.equal_range(3);
        if(mapPair.first == mapPair.second)
                cout <<"key 3 not find\n";
        else
                cout <<"key 3 fount\n";


}

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

#include <map>
#include <string>
#include <iostream>

using namespace std;

int main()
{

        map<int, string> mapStudent;

        mapStudent.insert(pair<int, string>(1, "student_one"));
        mapStudent.insert(pair<int, string>(2, "student_two"));
        mapStudent.insert(pair<int, string>(3, "student_three"));

        map<int, string>::reverse_iterator riter;

        for(riter = mapStudent.rbegin(); riter != mapStudent.rend(); riter++)
                cout << riter->first << " " << riter->second << endl;

}

 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

#include <map>
#include <string>
#include <iostream>

using namespace std;

int main()
{
        map<int, string> mapStudent;

        mapStudent.insert(pair<int, string>(1, "student_one"));
        mapStudent.insert(pair<int, string>(3, "student_two"));
        mapStudent.insert(pair<int, string>(5, "student_three"));

        map<int, string>::iterator iter;

        cout << "\nthe BILL of all student" << endl;
        for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
                cout << iter->first << " " << iter->second << endl;
        cout << "--------------------------" << endl;

        //by iterator
        iter = mapStudent.find(1);
        mapStudent.erase(iter);
        for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
                cout << "\t" << iter->first << " " << iter->second << endl;

        //by key
        mapStudent.insert(pair<int, string>(1, "student_one"));
        cout << "\nthe BILL of all student" << endl;
        for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
                cout << iter->first << " " << iter->second << endl;
        cout << "--------------------------" << endl;

        int rt = 0;
        rt = mapStudent.erase(1);
        cout << "erase(1):" << rt << endl;
        rt = mapStudent.erase(2);
        cout << "erase(2):" << rt << endl;
        for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
                cout << "\t" << iter->first << " " << iter->second << endl;

        //delete a range item
        mapStudent.insert(pair<int, string>(1, "student_one"));
        cout << "\nthe BILL of all student" << endl;
        for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
                cout << iter->first << " " << iter->second << endl;
        cout << "--------------------------" << endl;
        mapStudent.erase(mapStudent.begin(), mapStudent.end());
        //Removes the elements in the range [first; last).
        for(iter = mapStudent.begin(); iter != mapStudent.end(); iter ++)
                cout << "\t" << iter->first << " " << iter->second << endl;
}

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。

#include <map>
#include <iostream>
#include <string>
using namespace std;
typedef struct tagStudentInfo {
        int nID;
        string strName;

        /* in map, the sort need "<" for sorting, so this needed  */
        bool operator < (tagStudentInfo const& _A) const {
                if(nID < _A.nID) return true;
                if(nID == _A.nID) return strName.compare(_A.strName) < 0;
                return false;
        }
}StudentInfo, *PStudentInfo;

int main()
{
        int nSize;

        map<StudentInfo, int>mapStudent;
        map<StudentInfo, int>::iterator iter;
        StudentInfo studentInfo;

        studentInfo.nID = 1;
        studentInfo.strName = "student_one";
        mapStudent.insert(pair<StudentInfo, int>(studentInfo, 90));

        studentInfo.nID = 2;
        studentInfo.strName = "student_two";
        mapStudent.insert(pair<StudentInfo, int>(studentInfo, 80));

        studentInfo.nID = 3;
        studentInfo.strName = "student_three";
        mapStudent.insert(pair<StudentInfo, int>(studentInfo, 95));

        cout << "ID\tName\t\tScore\n";
        for (iter = mapStudent.begin(); iter != mapStudent.end(); iter++ )
                cout    << iter->first.nID <<"\t"
                        << iter->first.strName <<"\t"
                        << iter->second <<endl ;
}

第二种

#include <map>
#include <iostream>
#include <string>
using namespace std;
typedef struct tagStudentInfo {
        int nID;
        string strName;
}StudentInfo, *PStudentInfo;

class BySort{
        public:
                bool operator()
                (StudentInfo const &_A, StudentInfo const &_B) const
                {
                        if(_A.nID < _B.nID)
                                return true;
                        if(_A.nID == _B.nID)
                                return _A.strName.compare(_B.strName) < 0;
                        return false;
                }
};
int main()
{
        int nSize;

        map<StudentInfo, int, BySort>mapStudent;
        map<StudentInfo, int>::iterator iter;
        StudentInfo studentInfo;

        studentInfo.nID = 1;
        studentInfo.strName = "student_one";
        mapStudent.insert(pair<StudentInfo, int>(studentInfo, 90));

        studentInfo.nID = 2;
        studentInfo.strName = "student_two";
        mapStudent.insert(pair<StudentInfo, int>(studentInfo, 80));

        studentInfo.nID = 3;
        studentInfo.strName = "student_three";
        mapStudent.insert(pair<StudentInfo, int>(studentInfo, 95));

        cout << "ID\tName\t\tScore\n";
        for (iter = mapStudent.begin(); iter != mapStudent.end(); iter++ )
                cout    << iter->first.nID <<"\t"
                        << iter->first.strName <<"\t"
                        << iter->second <<endl ;
}

参考：

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