测试析构函数、虚函数、纯虚函数：

void testClass5() {
	class Parent {
		public:
			Parent(int x) { cout << "Parent构造: " << x << endl; }

			~Parent() {
				cout << "调用Parent析构函数" << endl;
			}

			virtual string toString() { // 虚函数
				return "i am Parent";
			}

			virtual int getAge() const = 0; // =0 标记为纯虚函数
		};

	class Child : public Parent {
		private:
			int a;
			string b;
		public:
			// 调用父类构造 + 初始化子类成员
			Child(int x, int val, const string& s) : Parent(x), a(val), b(s) {
				cout << "Child构造: " << a << ", " << b << endl;
			}

			~Child() {
				cout << "调用Child析构函数" << endl;
			}

			string toString() override {
				return "i am Child";
			}

			int getAge() const override {
				return 18;
			}
		};

		Child child(10, 20, "hello");
		cout << "child toString:" << child.toString() << endl;
		cout << "child getAge:" << child.getAge() << endl;
		Parent* parent = &child;
		cout << "parent toString:" << parent->toString() << endl;
		cout << "parent getAge:" << parent->getAge() << endl;
}

打印：

可见，析构函数的调用顺序是和构造函数的调用顺序相反的。另外，纯虚函数有点像java的抽象方法。