c++中stl----map

1 map的本质

(1)关联式容器，键值对应

(2)增加和删除节点对迭代器的影响很小。

(3)对于迭代器来说不可以修改键值，只能修改对应的实值。

(4)map内部数据的祖居是自建一颗红黑树(或者说是平衡二叉树)，具有自动排序的功能。

2 map的查增删

(1)map的插入

#include <map>
#include <string>
#include <iostream>
using namespace std;

int main()
{
    //方式一 pair
    map<int,string> mapStudent;
    mapStudent.insert(pair<int,string>(1,"lan"));
    mapStudent.insert(pair<int,string>(2,"ji"));
    mapStudent.insert(pair<int,string>(1,"kjh"));
    map<int,string>::iterator iter;
    map<int,string>::iterator iter1;
    //方式二
    map<int string> mapStudent1;
    mapStudent1.insert(map<int,string>::value_type(1,"nihao"));
    mapStudent1.insert(map<int,string>::value_type(1,"ben"));
    for(iter=mapStudent.begin();iter!=mapStudent.end();iter++)
    {
        cout<<iter->first<<" "<<iter->second<<endl;
    }
    for(iter=mapStudent1.begin();iter!=mapStudent1.end();iter++)
    {
        cout<<iter->first<<" "<<iter->second<<endl;

    }
    return 0;     
}

2 map的遍历

#include <map>
#include <string>
#include <iostream>
using namespace std;

int main()
{
    map<int,string> mapStudent;
    mapStudent[1]="stu_one";
    mapStudent[1]="stu_two";
    mapStudent[1]="stu_three";
    map<int,string>::iterator iter = mapStudent.find(1);
    if(iter!=mapStudent.end())
    {
        cout<<"找到了 value="<<iter->second<<endl;
    }else
    {
        cout<<"没有找到"<<endl;
    }
    return 0;
}

3 map的删除

#include <map>
#include <string>
#include <iostream>
using namespace std;

int main()
{
    map<int,string> mapStudent;
    mapStudent[1]="stu_one";
    mapStudent[1]="stu_two";
    mapStudent[1]="stu_three";
    map<int,string>::iterator iter = mapStudent.begin();
    for(;iter!=mapStudent.end();)
    {
        if((*iter).sencond=="stu_one")
        {
            mapStudent.erase(iter++);//iter被erase以后就会失效 所以后面不能再有iter++
        }else
        {
            ++iter;
        }
    }
    for(iter=mapStudent1.begin();iter!=mapStudent1.end();iter++)
    {
        cout<<iter->first<<" "<<iter->second<<endl;

    }
    return 0;
}

4 map排序

默认按照key从小到大。从大到小greater 相反less

#include <map>
#include <string>
#include <iostream>
using namespace std;
int main()
{
    map<string,int,greater<string>> mapStudent;
    mapStudent['nisan']=90;
    mapStudent['nisan']=70;
    mapStudent['nisan']=80;
    map<string,int>::iterator iter = mapStudent.begin();
    for(iter=mapStudent.begin();iter!=mapStudent.end();iter++)
    {
        cout<<iter->first<<" "<<iter->second<<endl;
    }
    return 0;
}

自定义排序方式

#include <string>
#include <iostream>
using namespace std;
struct CmpByKeyLength
{
    bool operator()(const string &k1,const string&k2){
        return k1.length()<k2.length();
    }
};
int main()
{
    map<string,int,CmpByKeyLength>mapStudent;
    mapStudent['nisan']=90;
    mapStudent['nisan']=70;
    mapStudent['nisan']=80;
    map<string,int>::iterator iter = mapStudent.begin();
    for(iter=mapStudent.begin();iter!=mapStudent.end();iter++)
    {
        cout<<iter->first<<" "<<iter->second<<endl;
    }
    return 0;
}

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