stl----map in c++

1 The essence of map

(1) Associative container, key-value correspondence

(2) Adding and deleting nodes has little effect on the iterator.

(3) For iterators, the key value cannot be modified, only the corresponding real value can be modified.

(4) The ancestral home of the internal data of the map is a self-built red-black tree (or a balanced binary tree), which has the function of automatic sorting.

2 Map search, addition and deletion

(1) Insertion of map

 1 #include <map>
 2 #include <string>
 3 #include <iostream>
 4 using namespace std;
 5 
 6 int main()
 7 {
 8     //方式一 pair
 9     map<int,string> mapStudent;
10     mapStudent.insert(pair<int,string>(1,"lan"));
11     mapStudent.insert(pair<int,string>(2,"ji"));
12     mapStudent.insert(pair<int,string>(1,"kjh"));
13     map<int,string>::iterator iter;
14     map<int,string>::iterator iter1;
15     //方式二
16     map<int string> mapStudent1;
17     mapStudent1.insert(map<int,string>::value_type(1,"nihao"));
18     mapStudent1.insert(map<int,string>::value_type(1,"ben"));
19     for(iter=mapStudent.begin();iter!=mapStudent.end();iter++)
20     {
21         cout<<iter->first<<" "<<iter->second<<endl;
22     }
23     for(iter=mapStudent1.begin();iter!=mapStudent1.end();iter++)
24     {
25         cout<<iter->first<<" "<<iter->second<<endl;
26 
27     }
28     return 0;     
29 }

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2 traversal of map

 1 #include <map>
 2 #include <string>
 3 #include <iostream>
 4 using namespace std;
 5 
 6 int main()
 7 {
 8     map<int,string> mapStudent;
 9     mapStudent[1]="stu_one";
10     mapStudent[1]="stu_two";
11     mapStudent[1]="stu_three";
12     map<int,string>::iterator iter = mapStudent.find(1);
13     if(iter!=mapStudent.end())
14     {
15         cout<<"找到了 value="<<iter->second<<endl;
16     }else
17     {
18         cout<<"没有找到"<<endl;
19     }
20     return 0;
21 }

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3 Deletion of map

 1 #include <map>
 2 #include <string>
 3 #include <iostream>
 4 using namespace std;
 5 
 6 int main()
 7 {
 8     map<int,string> mapStudent;
 9     mapStudent[1]="stu_one";
10     mapStudent[1]="stu_two";
11     mapStudent[1]="stu_three";
12     map<int,string>::iterator iter = mapStudent.begin();
13     for(;iter!= mapStudent.end();)
 14      {
 15          if ((*iter).sencond== " stu_one " )
 16          {
 17              mapStudent.erase(iter++);//iter will fail after being erased, so later no more iter++
 18          } else 
19          {
 20              ++ iter;
 21          }
 22      }
 23      for (iter=mapStudent1.begin();iter!=mapStudent1.end();iter++ )
 24      {
 25          cout<<iter->first << "  " <<iter->second<< endl;
26 
27     }
28     return 0;
29 }

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4 map sorting

By default, keys are sorted from small to large. From big to small, greater is the opposite of less

 1 #include <map>
 2 #include <string>
 3 #include <iostream>
 4 using namespace std;
 5 int main()
 6 {
 7     map<string,int,greater<string>> mapStudent;
 8     mapStudent['nisan']=90;
 9     mapStudent['nisan']=70;
10     mapStudent['nisan']=80;
11     map<string,int>::iterator iter = mapStudent.begin();
12     for(iter=mapStudent.begin();iter!=mapStudent.end();iter++)
13     {
14         cout<<iter->first<<" "<<iter->second<<endl;
15     }
16     return 0;
17 }

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custom sorting

 1 #include <string>
 2 #include <iostream>
 3 using namespace std;
 4 struct CmpByKeyLength
 5 {
 6     bool operator()(const string &k1,const string&k2){
 7         return k1.length()<k2.length();
 8     }
 9 };
10 int main()
11 {
12     map<string,int,CmpByKeyLength>mapStudent;
13     mapStudent['nisan']=90;
14     mapStudent['nisan']=70;
15     mapStudent['nisan']=80;
16     map<string,int>::iterator iter = mapStudent.begin();
17     for(iter=mapStudent.begin();iter!=mapStudent.end();iter++)
18     {
19         cout<<iter->first<<" "<<iter->second<<endl;
20     }
21     return 0;
22 }

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