c++单例模式

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1.基本实现

class Singleton{public:    static Singleton *Instance()    {        if (!spInstance)        {            spInstance = new Singleton;        }        return spInstance;    }protected:    Singleton() { }    ~Singleton()    {        if (spInstance)        {            delete spInstance;        }    }private:    static Singleton *spInstance;};Singleton *Singleton::spInstance = nullptr;

2.单例模板
singleton.h

#ifndef SINGLETON_H#define SINGLETON_Htemplate<typename T>class Singleton{public:    static T &Instance()    {        static T sInstance;        return sInstance;    }private:    Singleton() { }    Singleton(const Singleton &);    Singleton &operator=(const Singleton &);};#endif

main.cpp

#include <iostream>#include "singleton.h"using namespace std;class Example{public:    Example() { }    ~Example() { }    void Print();};void Example::Print(){    cout << "Example.Print()" << endl;}int main(){    Singleton<Example>::Instance().Print();}

3.改进的单例模板

singleton.h

#ifndef SINGLETON_H#define SINGLETON_Htemplate<typename T>class Singleton{public:    static T &Instance()    {        static T sInstance;        return sInstance;    }protected:    Singleton() { }    virtual ~Singleton() { }private:    Singleton(const Singleton &);    Singleton &operator=(const Singleton &);};#endif

main.cpp

#include <iostream>#include "singleton.h"using namespace std;class Example : public Singleton<Example>{    friend class Singleton<Example>;public:    void Print();private:    Example() { }    virtual ~Example() { }};void Example::Print(){    cout << "Example.Print()" << endl;}int main(){    Example::Instance().Print();}

4.带参数的单例模板
singleton.h

#ifndef SINGLETON_H#define SINGLETON_H#include <utility>template<typename T>class Singleton{public:    template<typename... Args>    static void CreateInstance(Args&&... args)    {        spInstance = new T(std::forward<Args>(args)...);    }    static T *Instance()    {        return spInstance;    }    static void DestroyInstance()    {        if (spInstance)        {            delete spInstance;            spInstance = nullptr;        }    }protected:    Singleton() { }    virtual ~Singleton() { }private:    Singleton(const Singleton &);    Singleton &operator=(const Singleton &);private:    static T *spInstance;};template<typename T>T *Singleton<T>::spInstance = nullptr;#endif

main.cpp

#include <iostream>#include "singleton.h"using namespace std;class Example : public Singleton<Example>{    friend class Singleton<Example>;public:    void Print();private:    Example(int i) { member = i; }    virtual ~Example() { }private:    int member;};void Example::Print(){    cout << "Example.Print(), member = " << member << endl;}int main(){    Example::CreateInstance(3);    Example::Instance()->Print();    Example::DestroyInstance();}

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