关联式容器map/multimap之初始化、删除元素、交换元素及清空操作

#include <iostream>
#include <map>
using namespace std;

typedef pair<int, double> mypair;

void print(map<int, double, less<int>> &m)
{
	map<int, double, less<int>>::iterator it;
	mypair tmp;
	if (m.size() < 0)
		cout << "Map is empty!" << endl;
	else
	{
		for (it = m.begin(); it != m.end(); it++)
		{
			tmp = *it;
			cout << tmp.first << ";" << tmp.second << endl;
		}
	}
}
void main()
{
	map<int, double, less<int>> m1, m2;
	// 初始化容器
	m1.insert(mypair(1, 6.0));
	m1.insert(mypair(2, 13.5));
	m1.insert(mypair(3, 11.3));
	m1.insert(mypair(4, 13.4));
	m1.insert(mypair(5, 15.1));

	// 输出容器内容
	cout << "m1:" << endl;
	print(m1);
	cout << "Size of m1:" << m1.size() << endl;

	// ------------- 容器的删除操作 -------------------------
	m2 = m1;
	m2.erase(2); // 原型：iterator erase(iterator it);
	cout << "m2:" << endl;
	print(m2);
	cout << "Size of m2 after erase(2):" << m2.size() << endl;

	m2.erase(m2.begin());// Iterator erase(iterator first, iterator last);
	cout << "m2 after erase(itrator_it):" << endl;
	print(m2);
	cout << endl;
	// Size_type erase(const Key &key);


	// ------------ 容器的元素交换操作 ----------------------
	/* void swap(map &str);
       容器Map/Multimap还提供了元素交换函数swap()。参与交换的两个对象必须类型一致。*/
	m1.swap(m2);
	cout << "m1:" << endl;
	print(m1);
	cout << "m2" << endl;
	print(m2);
	cout << endl;

	// --------------- 容器的清空操作 -----------------------
	m2.clear();
	cout << "m2 after clear():" << endl;
	print(m2);
	cout << "Size of m2 after clear:" << m2.size() << endl;
	cin.get();
}

编译结果：