c++中的单例类模板的实现方法详解

#include <iostream>
#include <string>

using namespace std;

class SObject
{
  static SObject* c_instance; // 定义标识符指针；

  /* 不需用拷贝和赋值，在单例模式中，始终只有一个对象 */  
  SObject(const SObject&);
  SObject& operator= (const SObject&);
  
  SObject() // 私有的构造函数
  {
  }
public:
  static SObject* GetInstance();  // 创建对象的入口
  
  void print()
  {
    cout << "this = " << this << endl;
  }
};

SObject* SObject::c_instance = NULL; // 静态成员类内声明，类外定义

SObject* SObject::GetInstance() // 单例模式的关键
{
  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();  // this = 0x940a008
  s1->print(); // this = 0x940a008
  s2->print(); // this = 0x940a008
  
  return 0;
}
// 注：单例模式中，对象的生命周期存在整个系统运行过程中，所以是绝对不释放的；

 // 对上个单例模式实现代码的改进

// singleton.hpp 单例模式代码
#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

// main.cpp 测试文件
#include <iostream>
#include <string>
#include "singleton.hpp"

using namespace std;

class SObject
{
  friend class Singleton<SObject>;  // 当前类需要使用单例模式
  
  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();  // 0xe63c20
  s1->print(); // 0xe63c20
  s2->print(); // 0xe63c20
  
  return 0;
}