单例模式扩展之多例缓存的设计

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缓存我们主要采用std::map和懒汉式单例模式进行设计。本文中暂不考虑线程安全的问题。
源码：

#include <iostream>
#include <map>
#include <string>

using namespace std;

// 缓存的实例个数
const static int MAX_NUM = 5;
class Singleton;
static map<int, Singleton *> CacheMap = map<int, Singleton *>();

class Singleton
{
public:
    static Singleton *getInstance() {
        m_singleton = CacheMap[m_instanceCount];

        if (m_singleton == nullptr) {
                m_singleton = new Singleton;
                CacheMap[m_instanceCount] = m_singleton;
        }
        ++ m_instanceCount;
        if (m_instanceCount > MAX_NUM) {
                m_instanceCount = 1;
        }
        return m_singleton;
    }

private:
    Singleton() {
            m_singleton = nullptr;
            cout << "正在构建 Singleton" << endl;
    }

private:
    static Singleton *m_singleton;
    static int m_instanceCount; // 存放的实例的个数
};

Singleton *Singleton::m_singleton = nullptr;
int Singleton::m_instanceCount = 1;

int main() 
{
    Singleton* p1 = Singleton::getInstance();
    Singleton* p2 = Singleton::getInstance();
    Singleton* p3 = Singleton::getInstance();
    Singleton* p4 = Singleton::getInstance();
    Singleton* p5 = Singleton::getInstance();
    printf("p1=%x,p2=%x,p3=%x,p4=%x,p5=%x\n", p1, p2, p3, p4, p5);
    Singleton* p6 = Singleton::getInstance();
    Singleton* p7 = Singleton::getInstance();
    Singleton* p8 = Singleton::getInstance();
    Singleton* p9 = Singleton::getInstance();
    Singleton* p10 = Singleton::getInstance();
    printf("p6=%x,p7=%x,p8=%x,p9=%x,p10=%x\n", p6, p7, p8, p9, p10);
    system("pause");
    return 0;
}

打印结果：

正在构建 Singleton
正在构建 Singleton
正在构建 Singleton
正在构建 Singleton
正在构建 Singleton
p1=577d90,p2=57ef58,p3=57ef88,p4=576180,p5=5761b0
p6=577d90,p7=57ef58,p8=57ef88,p9=576180,p10=5761b0
请按任意键继续. . .