STL tutorial 8-map

map

map be relative to set difference ,map With key value and real value , All elements are automatically sorted according to the key value .pair The first element of is called the key value , The second element is called a real value .map It also takes the red black tree as the underlying implementation mechanism .

map Four insertion methods

	map<int, int> mymap;// Statement map, The first parameter key type , The second parameter value type 
	mymap.insert(pair<int, int>(10, 10));// The first way to insert 
	mymap.insert(make_pair(20, 20));// The second insertion method 
	mymap.insert(map<int, int>::value_type(30, 30));// The third kind of 
	mymap[40] = 40;// A fourth 


	// Print 
	for (map<int, int>::iterator it = mymap.begin(); it != mymap.end(); it++)
	{
    
		//*it What comes out is pair
		cout << "key:" << (*it).first << "value:" << it->second << endl;
	}

Note the fourth insertion method above , If no access is inserted , such as cout Print mymap[40], At this time, it will also be inserted , Because the value type is int, So... Will be inserted 0

Add custom type

Add a class here

class MyKey
{
    
public:
	MyKey(int index, int id)
	{
    
		this->mIndex = index;
		this->mID = id;
	}
public:
	int mIndex;
	int mID;
};

Define comparison type

struct mycompare
{
    
	bool operator()(const MyKey& key1, const MyKey& key2)const
	{
    
		return key1.mIndex > key2.mIndex;
	}
};

Additive elements

	map<MyKey, int, mycompare> mymap;// Automatic sorting , Tell him how to sort 
	mymap.insert(make_pair(MyKey(1, 2), 10));
	mymap.insert(make_pair(MyKey(4, 5), 20));

Print elements

	for (auto it = mymap.begin(); it != mymap.end(); it++)
	{
    
		cout << it->first.mIndex << ":" << it->first.mID << "=" << it->second << endl;
	}