订阅本文为【C++设计模式之Singleton】的汉字拼音对照版显示拼音
一yi、功gong能neng 保bao证zheng一yi个ge类lei仅jin有you一yi个ge实shi例li。 三san、优you缺que点dianSingleton模mo式shi是shi做zuo为wei"全quan局ju变bian量liang"的de替ti代dai品pin出chu现xian的de。所suo以yi它ta具ju有you全quan局ju变bian量liang的de特te点dian：全quan局ju可ke见jian、贯guan穿chuan应ying用yong程cheng序xu的de整zheng个ge生sheng命ming期qi，它ta也ye具ju有you全quan局ju变bian量liang不bu具ju备bei的de性xing质zhi：同tong类lei型xing的de对dui象xiang实shi例li只zhi可ke能neng有you一yi个ge。四si、实shi现xian
教jiao科ke书shu上shang的deSingleton定ding义yi如ru下xia：
class Singleton
{
public:
static Singleton* Instance() ;
protected:
Singleton() {}
private:
static Singleton *_instance ;
Singleton(const Singleton&) ;
Singleton& operator=(const Singleton&) ;
} ;
Singleton* Singleton::_instance = NULL ;
Singleton* Singleton::Instance()
{
(_instance == NULL) ? _instance = new Singleton() : 0 ; //lazy initialization
return _instance ;
}
(1)因yin为wei返fan回hui的de是shi指zhi针zhen，为wei防fang止zhi用yong户hu调tiao用yongdelete函han数shu，可ke把bastatic Singleton *_instance；改gai为wei在zaiInstance()中zhong定ding义yistatic Singleton _instance。这zhe样yang显xian然ran更geng安an全quan，同tong时shi也ye具ju有youlazy initialization的de特te性xing(即ji第di一yi次ci访fang问wen时shi才cai创chuang建jian)。
(2)假jia设she需xu要yao从congSingleton派pai生sheng子zi类lei，而er子zi类lei也ye需xu要yao有you同tong样yang的de性xing质zhi，既ji只zhi能neng创chuang建jian一yi个ge实shi例li。我wo觉jiao得de，这zhe很hen难nan办ban。根gen本ben原yuan因yin在zai于yuInstance()函han数shu不bu是shi虚xu函han数shu，不bu具ju有you多duo态tai的de性xing质zhi。一yi种zhong常chang用yong方fang法fa是shi把baInstance()函han数shu移yi到dao子zi类lei中zhong，这zhe时shi就jiu只zhi能neng用yongstatic Singleton *_instance，而er不bu能neng用yongstatic Singleton _instance了le，除chu非fei把ba_instance也ye要yao移yi到dao子zi类lei，无wu论lun怎zen么me做zuo都dou不bu优you雅ya。另ling一yi种zhong方fang法fa是shi用yong模mo板ban。具ju体ti用yong什shen么me方fang法fa，只zhi能neng根gen据ju实shi际ji情qing况kuang权quan衡heng。
五wu、示shi例li代dai码ma
(1)没mei子zi类lei的de情qing况kuang
namespace DesignPattern_Singleton
{
class Singleton
{
public:
static Singleton* Instance() { static Singleton _instance ; return &_instance ; }
protected:
Singleton() {}
private:
Singleton(const Singleton&) ;
Singleton& operator=(const Singleton&) ;
} ;
}
客ke户hu端duan代dai码ma：
{
using namespace DesignPattern_Singleton ;
Singleton *p = Singleton::Instance() ;
......
}
(2)有you子zi类lei的de情qing况kuang
方fang法fa一yi：
namespace DesignPattern_Singleton
{
// class Singleton
class Singleton
{
protected:
Singleton() {}
static Singleton *_instance ;
private:
Singleton(const Singleton&) ;
Singleton& operator=(const Singleton&) ;
} ;
Singleton* Singleton::_instance = NULL ;
// class ConcreteSingleton
class ConcreteSingleton : public Singleton
{
public:
static Singleton* Instance() ;
protected:
ConcreteSingleton() {}
} ;
Singleton* ConcreteSingleton::Instance()
{
(_instance == NULL) ? _instance = new ConcreteSingleton() : 0 ;
return _instance ;
}
}
客ke户hu端duan代dai码ma：
{
using namespace DesignPattern_Singleton ;
Singleton *p = ConcreteSingleton::Instance() ;
}
方fang法fa二er：
namespace DesignPattern_Singleton
{
// class Singleton
class Singleton
{
protected:
Singleton() {}
private:
Singleton(const Singleton&) ;
Singleton& operator=(const Singleton&) ;
} ;
// class ConcreteSingleton
class ConcreteSingleton : public Singleton
{
public:
static Singleton* Instance() { static ConcreteSingleton _instance ; return &_instance ; }
protected:
ConcreteSingleton() {}
} ;
}
客ke户hu端duan代dai码ma：
{
using namespace DesignPattern_Singleton ;
Singleton *p = ConcreteSingleton::Instance() ;
}
方fang法fa三san：
namespace DesignPattern_Singleton
{
template < class T >
class Singleton
{
public:
static T* Instance() { static T _instance ; return &_instance ; }
protected:
Singleton() {}
private:
Singleton(const Singleton &) ;
Singleton& operator=(const Singleton&) ;
} ;
class ConcreteSingleton : public Singleton< ConcreteSingleton > {} ;
}
客ke户hu端duan代dai码ma
{
using namespace DesignPattern_Singleton ;
ConcreteSingleton *p = ConcreteSingleton::Instance() ;
}【原文】
