01C++实现单例模式

#include <iostream>#include <string>#include <vector>#include <list>using namespace std;// 使用场景：// 在应用系统开发中，我们常常有以下需求：// - 在多个线程之间，比如初始化一次socket资源；比如servlet环境，共享同一个资源或者操作同一个对象// - 在整个程序空间使用全局变量，共享资源// - 大规模系统中，为了性能的考虑，需要节省对象的创建时间等等。// 因为Singleton模式可以保证为一个类只生成唯一的实例对象，所以这些情况，Singleton模式就派上用场了。// 步骤：// 1. 构造函数私有化// 2. 提供一个全局的静态方法（全局访问点）// 3. 在类中定义一个静态指针，指向本类的变量的静态变量指针// ---------------------------------------------------------// 懒汉式class Singleton1 {public:  static Singleton1* GetInstance() {    if (singleton_ == NULL) {      singleton_ = new Singleton1;    }    return singleton_;  }  static void DestreyInstance() {    if (singleton_ != NULL) {      delete singleton_;    }  }private:  // 防止外部构造。  Singleton1() {}  // 防止拷贝和赋值。  Singleton1& operator=(const Singleton1&);  Singleton1(const Singleton1& singleton1) {}private:  static Singleton1* singleton_;};Singleton1* Singleton1::singleton_ = NULL;// ---------------------------------------------------------// 饿汉式class Singleton2 {public:  static Singleton2* GetInstance() {    return singleton_;  }  static void DestreyInstance() {    if (singleton_ != NULL) {      delete singleton_;    }  }private:  // 防止外部构造。  Singleton2() {}  // 防止拷贝和赋值。  Singleton2& operator=(const Singleton2&);  Singleton2(const Singleton2& singleton2) {}private:  static Singleton2* singleton_;};Singleton2* Singleton2::singleton_ = new Singleton2;int main08() {  Singleton1* s11 = Singleton1::GetInstance();  Singleton1* s12 = Singleton1::GetInstance();  if (s11 == s12) {    cout << "s11 : " << s11 << "  s12 : " << s12 << endl;    cout << "s11 == s12" << endl;  }  Singleton2* s21 = Singleton2::GetInstance();  Singleton2* s22 = Singleton2::GetInstance();  if (s21 == s22) {    cout << "s21 : " << s21 << "  s22 : " << s22 << endl;    cout << "s21 == s22" << endl;  }  Singleton1::DestreyInstance();  Singleton2::DestreyInstance();  return 0;}