面试题2：实现Singleton模式

书上给的是C#实现，自己写几个C++实现：

1. 基本版，适用于单线程

 1 class Singleton
 2 {
 3 public:
 4     static Singleton * Instance();
 5     static void Destroy();
 6 protected:
 7     Singleton(){}
 8 private:
 9     static Singleton * m_pInstance;
10 };
11 
12 Singleton * Singleton::m_pInstance = NULL;
13 
14 Singleton * Singleton::Instance()
15 {
16     if (m_pInstance == NULL)
17         m_pInstance = new Singleton;
18     return m_pInstance;
19 }
20 
21 void Singleton::Destroy()
22 {
23     delete m_pInstance;
24 }

2. 多线程，使用加锁机制

利用winAPI中的加锁

 1 #include <Windows.h>
 2 
 3 class Locker
 4 {
 5 protected:
 6     friend class Singleton;
 7     CRITICAL_SECTION cs;
 8 
 9 public:
10     Locker(){
11         ::InitializeCriticalSection(&cs);
12     }
13     void lock(){
14         ::EnterCriticalSection(&cs);
15     }
16     void unlock(){
17         ::LeaveCriticalSection(&cs);
18     }
19     ~Locker(){
20         ::DeleteCriticalSection(&cs);
21     }
22 };
23 
24 class Singleton
25 {
26 public:
27     static Singleton * Instance();
28     static void Destroy();
29 protected:
30     Singleton(){}
31 private:
32     static Singleton * m_pInstance;
33 };
34 
35 Singleton * Singleton::m_pInstance = NULL;
36 
37 Singleton * Singleton::Instance()
38 {
39     Locker *lock = new Locker;
40     lock->lock();
41     if (m_pInstance == NULL)
42         m_pInstance = new Singleton;
43     lock->unlock();
44     return m_pInstance;
45 }
46 
47 void Singleton::Destroy()
48 {
49     delete m_pInstance;
50 }

3. 模版实现

 1 class Singleton
 2 {
 3 public:
 4     static T * Instance();
 5     static void Destroy();
 6 protected:
 7     Singleton(){}
 8 private:
 9     static T * m_pInstance;
10 };
11 
12 template <typename T>
13 T * Singleton<T>::m_pInstance = NULL;
14 
15 template <typename T>
16 T * Singleton<T>::Instance()
17 {
18     if (m_pInstance == NULL)
19         m_pInstance = new T;
20     return m_pInstance;
21 }
22 
23 template <typename T>
24 void Singleton<T>::Destroy()
25 {
26     delete m_pInstance;
27 }

参考资料：

http://blog.csdn.net/a342374071/article/details/18270643/

http://www.cnblogs.com/liyuan989/p/4264889.html