Map container

One 、 Insert the way

 map<int, int> m;
    // The first way to insert 
    m.insert(pair<int, int>(1, 10));
    // The second insertion method 
    m.insert(make_pair(2, 20));
    // Third insertion method 
    m.insert(map<int, int>::value_type(3, 30));
    // Fourth insertion method 
    m[4] = 40;

result

key = 1 value = 10
key = 2 value = 20
key = 3 value = 30
key = 4 value = 40

Be careful
If key = 1 value = 10 Already exist , How to change ？

    map<int, int> m;
    // The first way to insert 
    m.insert(pair<int, int>(1, 10));
    m.insert(pair<int, int>(1, 12));
    // The second insertion method 
    m.insert(make_pair(1, 20));
    // Third insertion method 
    m.insert(map<int, int>::value_type(1, 30));
    // Fourth insertion method 
    //m[1] = 40;
    printMap(m);

Running results
key = 1 value = 10

So we need to change it in the fourth way ：m[1] = 40;

Two 、 Traverse （ Using iterators ）

void printMap(map<int, int>& m)
{
    
    for (map<int, int>::iterator it = m.begin(); it != m.end(); it++)
    {
    
        cout << "key = " << it->first << " value = " << it->second << endl;
    }
    cout << endl;
}

map<int, int>::iterator it -> Define an iterator it
it->first map Container of key value
it->second map Container of value value