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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