需求：有时遇到某些类特征相似而又没有共同的父类，希望能够知道这些类的创建数量之和。
思路：将这些类继承自同一个计数类，共享计数变量s_createCount信息，实现如下：

class Counter
{
public:
	Counter() {
		++s_createCount;
		++s_aliveCount;
		std::cout << "Class Created Count = " << s_createCount << " Class Alive Count = " << s_aliveCount << std::endl;
	}
	~Counter() {
		--s_aliveCount;
		std::cout << "Class Alive Count = " << s_aliveCount << std::endl;
	}

private:
	static int s_createCount;
	static int s_aliveCount;
};

int Counter::s_createCount = 0;
int Counter::s_aliveCount = 0;

class CounterA : public Counter{};
class CounterB : public Counter {};

int main()
{
	CounterA ca;
	CounterB cb;
	{
		CounterA ca2;
	}
	system("pause");
	return 0;
}

需求：有时遇到某些类，希望能够分别知道各个类的创建数量信息（兼容需求1）。
思路：既然继承同一个类会导致共享静态数据，那么可以依靠类模板的特性（只要模板参数不同，类就不同），继承不同的类，实现如下：

template <typename T>
class Counter
{
public:
	Counter() {
		++s_createCount;
		++s_aliveCount;
		std::cout << __FUNCTION__ << "Class Created Count = " << s_createCount << " Class Alive Count = " << s_aliveCount << std::endl;
	}

	~Counter() {
		--s_aliveCount;
		std::cout << __FUNCTION__ << "Class Alive Count = " << s_aliveCount << std::endl;
	}

private:
	static int s_createCount;
	static int s_aliveCount;
};

template <typename T>
int Counter<T>::s_createCount = 0;
template <typename T>
int Counter<T>::s_aliveCount = 0;

// 这里不必考虑CRTP易错点（兼容需求1）：派生的基类模板参数不是派生类
// 允许class CounterB : public Counter<CounterA> {};的情况存在
// 因为不涉及将模板参数T转换为派生类的操作
class CounterA : public Counter<CounterA> {};
class CounterB : public Counter<CounterB> {};

int main()
{
	CounterA ca;
	CounterB cb;
	CounterC cc;
	{
		CounterA ca2;
	}
	system("pause");
	return 0;
}