STL map operation

#include<iostream>
#include<map>
#include<algorithm>
#include<functional>
using namespace std;  
void MapDelete()
{
    typedef pair<int, char> in_pair;
    map<int, char> db;// Result default key value sorting from small to large .
    //map<int, char,greater<int>> db;// The result is modified to sort the key values from large to small .

    db.insert(in_pair(1, 'a'));
    db.insert(in_pair(2, 'a'));
    db.insert(in_pair(3, 'a'));
    db.insert(in_pair(4, 'a'));

     Iterative output
    //map<int, char>::iterator ite = db.begin();
    map<int, char,greater<int>>::iterator ite = db.begin();// The result is modified to sort the key values from large to small .
    //ite++;
    //ite++;
     Delete
    db.erase(ite);// The delete key value is 3 Value
    //db.erase(3);// The delete key value is 3 Value
    db.erase(ite, db.end());// The delete key value is 3 Value to the end of the tail .
    //ite = db.begin();// After modification, the iterator will fail , So we need to restate .
    /*for ( ite ; ite != db.end(); ite++)
    {
        cout << ite->first << " " << ite->second << endl;
    }*/

    // Iterator lookup .
    map<int, char>::iterator ite = db.begin();
    map<int, char>::iterator ite1 = db.find(2);// lookup 2 This key value , Finding it will return 2 The iterator at the location .

if (db.end() == db.find(6)) // If there is no 6 This key value , be find Return to the last element end()（ Not the last key , But next to the actual tail element end()）, The operation will crash .
    {
        cout << "OK" << endl;
    }
    cout << ite1->first << " " << ite1->second << endl;

    cout << db.lower_bound(3)->first << endl;// Returns the parameter key The location of , This position is greater than or equal to key：key<=pos.
    cout << db.upper_bound(3)->first << endl;// Returns the parameter key Next position of , This position is greater than key：key<pos.
 

}
int main()
{
    
    //MapOther();
    MapDelete();
    system("pause");
    return 0;
}

* Key values cannot be modified （ Caused by red and black trees ）, The actual value can be modified , Changing the key value will change the whole structure .