C++单例模式（线程安全）

懒汉模式

#include  
#include  
using namespace std; 
template<class T> 
class A { 
  public: 
	A(A&) = delete; 
	A& operator=(const A&) = delete;
	static T* Instance(); 
	static T* p; 
	static mutex mu; 
  protected: 
	A() = default; 
}; 

template<class T> 
T* A<T>::p = NULL; 

template<class T> 
mutex A<T>::mu; 

template<class T> 
T* A<T>::Instance() { 
	if (p == NULL) { 
		mu.lock(); 
		if (p == NULL) { 
			T* t = new T; 
			p = t; 
		} 
		mu.unlock(); 
	} 
	return p; 
} 

int main() { 
	int* ptr = A<int>::Instance(); 
	return 0; 
} 

饿汉模式

#include  
#include  
using namespace std; 
template<class T> 
class A { 
  public: 
	A(A&) = delete; 
	A& operator=(const A&) = delete;
	static T* Instance(); 
	static T* p; 
  protected: 
	A() = default; 
}; 

template<class T> 
T* A<T>::p = new T; 

template<class T> 
T* A<T>::Instance() { 
	return p; 
} 

int main() { 
	int* ptr = A<int>::Instance(); 
	return 0; 
}