单例

1.饿汉式

class singleton
{
protected:
  singleton(){}
private:
  static singleton* p;
public:
  static singleton* getInstance();
  static void destory()
  {
    if(p)
      delete p;
  }
private:
  ~singleton(){}
};
singleton* singleton::p = new singleton;//new后面加括号调用无参构造函数，加括号的调用默认的或唯一的构造函数。
singleton* singleton::getInstance()
{
  return p;
}