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

#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 ";

else

cout << "Insert Failure " ;

}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 " ;

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 ";

else

cout <<"key 2 fount ";

mapPair = mapStudent.equal_range(3);

if(mapPair.first == mapPair.second)

cout <<"key 3 not find ";

else

cout <<"key 3 fount ";

}

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 << " the 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 << " " << iter->first << " " << iter->second << endl;

//by key

mapStudent.insert(pair<int, string>(1, "student_one"));

cout << " the 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 << " " << iter->first << " " << iter->second << endl;

//delete a range item

mapStudent.insert(pair<int, string>(1, "student_one"));

cout << " the 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 << " " << 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 Name Score ";

for (iter = mapStudent.begin(); iter != mapStudent.end(); iter++ )

cout << iter->first.nID <<" "

<< iter->first.strName <<" "

<< 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 Name Score ";

for (iter = mapStudent.begin(); iter != mapStudent.end(); iter++ )

cout << iter->first.nID <<" "

<< iter->first.strName <<" "

<< iter->second <<endl ;

}

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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