单例类模板

Posted 2021-10-03 学习只为旅行

#include <iostream>
#include <string>

using namespace std;

class SObject
{
	//静态成员变量必须在类外初始化！
    static SObject* c_instance;
    
    SObject(const SObject&);
    SObject& operator= (const SObject&);
    
    SObject()
    {
    }
public:
    static SObject* GetInstance();
    
    void print()
    {
        cout << "this = " << this << endl;
    }
};

SObject* SObject::c_instance = NULL;

SObject* SObject::GetInstance()
{
    if( c_instance == NULL )
    {
        c_instance = new SObject();
    }
    
    return c_instance;
}

int main()
{
    SObject* s = SObject::GetInstance();
    SObject* s1 = SObject::GetInstance();
    SObject* s2 = SObject::GetInstance();
    
    s->print();
    s1->print();
    s2->print();
    
    return 0;
}

说明指向同一个对象

#ifndef _SINGLETON_H_
#define _SINGLETON_H_

template
< typename T >
class Singleton
{
    static T* c_instance;
public:
    static T* GetInstance();
};

template
< typename T >
T* Singleton<T>::c_instance = NULL;

template
< typename T >
T* Singleton<T>::GetInstance()
{
    if( c_instance == NULL )
    {
        c_instance = new T();
    }   
    return c_instance;
}
#endif

#include <iostream>
#include <string>
#include "Singleton.h"

using namespace std;

class SObject
{
	//友元概念
	//Singleton这个类就可以访问SObject这个类所有成员了！！！
    friend class Singleton<SObject>;    // 当前类需要使用单例模式
    //为什么要来一波友元的操作？
    //SObject* s = new SObject();这么写直接报错！说明在外部无法定义类对象啊，构造函数私有，所以报错！
    //那么声明友元后：SObject* s = Singleton<SObject>::GetInstance();
    //其中，GetInstance()会new一个SObject的对象出来（此时调用私有的构造函数），本应该报错，但是友元的原因，Singleton这个类
    //就可以访问SObject这个类所有成员了，不管构造函数私不私有，都不会报错！！！这里容易忘记之前的知识点！
    
    SObject(const SObject&);
    SObject& operator= (const SObject&);
    
    SObject()
    {
    }
public:
    
    void print()
    {
        cout << "this = " << this << endl;
    }
};

int main()
{
    SObject* s = Singleton<SObject>::GetInstance();
    SObject* s1 = Singleton<SObject>::GetInstance();
    SObject* s2 = Singleton<SObject>::GetInstance();
    
    s->print();
    s1->print();
    s2->print();
    
    return 0;
}

小结