Map container

1. map Constructor and assignment operation of container

because map The data stored in the container appears in pairs , So we need to use pair To help us complete storage

1.1 Constructors

 

Here we only consider copy construction

int main()
{
	//map The data in the container appears in pairs , The inserted data must be a pair of groups 
	map<string, int>m;
	m.insert(pair<string, int>(" Zhang San ", 18));
	m.insert(pair<string, int>(" Li Si ", 28));
	m.insert(pair<string, int>(" Wang Wu ", 17));
	m.insert(pair<string, int>(" Zhao er ", 32));
	Print(m);
	cout << "------------" << endl;

	// Copy structure 
	map<string, int>m1(m);
	Print(m1);

	return 0;
}

1.2 Assignment operation

Use = To help us complete the assignment

int main()
{
	//map The data in the container appears in pairs , The inserted data must be a pair of groups 
	map<string, int>m;
	m.insert(pair<string, int>(" Zhang San ", 18));
	m.insert(pair<string, int>(" Li Si ", 28));
	m.insert(pair<string, int>(" Wang Wu ", 17));
	m.insert(pair<string, int>(" Zhao er ", 32));
	Print(m);

	// Copy of assignment 
	cout << "------------" << endl;
	map<string, int>m2;
	m2 = m;
	Print(m2);
	return 0;
}

2. map Large capacity, small capacity and Exchange

2.1 Calculation of size

Here we use size function , It will return map The number of elements in the container

void Print(const map<int, int>& m)
{
	for (auto i = m.begin(); i != m.end(); i++)
	{
		cout << i->first << " " << i->second << endl;
	}
}

// Size calculation 
void test01()
{
	map<int, int>m1;

	for (int i = 0; i < 5; i++)
	{
		m1.insert(pair<int, int>(i, i));
	}
	Print(m1);
	if (m1.empty())
	{
		cout << "map The container is empty " << endl;
	}
	else
	{
		cout << "map The container is not empty " << endl;
		cout << " The size of the container is :" << m1.size() << endl;
	}
}

int main()
{
	test01();
	return 0;
}

 2.2 Exchange of containers

 swap Space between two containers can be exchanged

void Print(const map<int, int>& m)
{
	for (auto i = m.begin(); i != m.end(); i++)
	{
		cout << i->first << " " << i->second << endl;
	}
}
// Switching operation 
void test02()
{
	map<int, int>m1;

	for (int i = 0; i < 5; i++)
	{
		m1.insert(pair<int, int>(i, i));
	}

	Print(m1);

	map<int, int>m2;
	for (int i = 0; i < 3; i++)
	{
		m2.insert(pair<int, int>(i + 3, i + 3));
	}
	cout << "--------------" << endl;
	Print(m2);

	cout << " After exchanging " << endl;
	m1.swap(m2);
	Print(m1);
	cout << "--------------" << endl;

	Print(m2);
}
int main()
{
	test02();
	return 0;
}

 3. map The insertion and deletion of containers

3.1 map Insertion of container

  Here we mainly consider map How the container inserts data ：

The first one is

m.insert(pair<int, int>(1, 10));

The second kind

m.insert(make_pair(2, 20));

The third kind of

m.insert(map<int, int>::value_type(3, 30));

A fourth

m[4] = 40;

Added results :

  because map The container will insert the value according to Key value To sort , Because we only consider the way of insertion , Regardless of the insertion position

3.2 map Deletion of container

void Print(const map<int, int>& m)
{
	for (auto i = m.begin(); i != m.end(); i++)
	{
		cout <<"key = "<< i->first << " value = " << i->second << endl;
	}
}
void test01()
{
	map<int, int>m;
	// The first one is 
	m.insert(pair<int, int>(1, 10));

	// The second kind 
	m.insert(make_pair(2, 20));

	// The third kind of 
	m.insert(map<int, int>::value_type(3, 30));

	// A fourth 
	m[4] = 40;
	Print(m);
	cout << endl;
	//1. Delete by iterator 
	m.erase(m.begin());
	Print(m);
	cout << endl;

	//2. The delete key value is 3
	m.erase(3);
	Print(m);

	cout << endl;
	//3. Delete range [m.begin(),m.end()) All values 
	m.erase(m.begin(), m.end());
	Print(m);
}
int main()
{
	test01();
	return 0;
}

  Results after deletion :

 4. map Container search and Statistics

4.1 map Container lookup

  If you find the element you are looking for , Returns the iterator of the element , Otherwise return to map::end

void test01()
{
	map<int, int>m;
	m.insert(make_pair(1, 10));
	m.insert(make_pair(2, 20));
	m.insert(make_pair(3, 30));
	auto p = m.find(55);
	if (p == m.end())
	{
		cout << " Can't find " << endl;
	}
	else
	{
		cout << "first = " << p->first << " second = " << p->second;
	}
    p = m.find(3);
	if (p == m.end())
	{
		cout << " Can't find " << endl;
	}
	else
	{
		cout << "first = " << p->first << " second = " << p->second;
	}

}
int main()
{
	test01();
	return 0;
}

The operation results are as follows :

 4.2 map Statistics of containers

  Find key values k Whether there is , Return if present 1, Returns if it does not exist 0

void test01()
{
	map<int, int>m;
	m.insert(make_pair(1, 10));
	m.insert(make_pair(2, 20));
	m.insert(make_pair(3, 30));
	cout << m.count(3) << endl;
	cout << m.count(5) << endl;
}
int main()
{
	test01();
	return 0;
}

The operation results are as follows ：