Singleton,顧名思義,從字面上來理解就是單例模式,這是C++程序中
常用到的一種設計模式,特別是像文件管理器,紋理管理器這種整個軟件
中只需要唯一的實例來管理所有資源時,這種模式的價值便得以體現。
下面來介紹兩種用於派生管理的Singleton模式:
其中,第一種是Gof版本的Singleton, 其代碼如下:
//【Singleton_Gof.h】
#pragma once
template<typename T>
class Singleton_Gof
{
protected:
static T* ms_Singleton;
Singleton_Gof(){assert(!ms_Singleton);}
~Singleton_Gof(){assert(ms_Singleton);ms_Singleton=NULL;}
private:
Singleton_Gof(const Singleton_Gof&); //防止構造函數的複製
Singleton_Gof& operator=(const Singleton_Gof&);
public:
static T* getSingletonPtr(){if (!ms_Singleton)ms_Singleton = new T();return ms_Singleton;}
static T& getSingleton(){if (!ms_Singleton)ms_Singleton = new T();return (*ms_Singleton);}
};
template<typename T>T* Singleton_Gof<T>::ms_Singleton = NULL;
其大致上的原理便是在需要初始化時,將靜態的Singleton實例指向派生類T對象,
類似的,還有第二種Singleton, 其代碼如下:
//【Singleton.h】
#pragma once
#include <cassert>
template<typename T>
class Singleton
{
private:
Singleton(const Singleton<T>&);
Singleton& operator=(const Singleton<T> &);
protected:
static T* ms_Singleton;
Singleton(){
assert(!ms_Singleton);
#if defined( _MSC_VER ) && _MSC_VER < 1200
int offset = (int)(T*)1 - (int)(Singleton <T>*)(T*)1;
ms_Singleton = (T*)((int)this + offset);
#else
ms_Singleton = static_cast< T* >( this );
#endif
};
~Singleton(){assert(ms_Singleton); ms_Singleton = NULL;}
public:
static T& getSingleton(){if(!ms_Singleton)new T(); return (*ms_Singleton);}
static T* getSingletonPtr(){if(!ms_Singleton)new T(); return ms_Singleton;}
};
template<typename T>T* Singleton<T>::ms_Singleton = NULL;
Singleton()裏的代碼在OGRE和《遊戲編程精粹》都出現過,這裏涉及VC編譯器的內存對齊,就不詳細講解了,
然後我們便可以利用上面的Singleton()代碼派生出一個紋理管理器來,我這裏粗略寫了下:
//【TextureMgr.h】
#include <string>
#include <map>
#include <iostream>
#include "Singleton.h"
#include "Singleton_Gof.h"
using namespace std;
//Texture
class Texture
{
private:
string m_Name;
public:
Texture(const string name):m_Name(name){load();};
~Texture(){unload();}
const string& getName()const {return m_Name;}
bool load(){cout<<"加載了一張紋理:"+m_Name<<endl;return true;}
bool unload(){cout<<"從資源中清除一張紋理:"+m_Name<<endl;return true;}
void doSomeThing(){cout<<"對紋理:"+m_Name+",進行了某些操作"<<endl;}
};
typedef std::map<string, Texture*> texMap;
typedef texMap::iterator texMapIter;
#define SAFE_DELETE(p) {if(p){delete p;p=NULL;}}
//TextureMgrBase
class TextureMgrBase
{
texMap m_TiMap;
public:
Texture* getTexture(const string name)
{
texMapIter iter = m_TiMap.find(name);
if(iter == m_TiMap.end())
{
Texture* tex = new Texture(name);
m_TiMap.insert(std::make_pair(name, tex));
return tex;
}
else
{
return iter->second;
}
}
TextureMgrBase(){cout<<"TextureMgrBase constructor"<<endl;}
~TextureMgrBase(){
for(texMapIter iter = m_TiMap.begin();iter!=m_TiMap.end();iter++)
{
SAFE_DELETE(iter->second);
}
cout<<"TextureMgrBase destructor"<<endl;
}
};
//TextureMgr
class TextureMgr:public TextureMgrBase, public Singleton<TextureMgr>{
public:
TextureMgr(){cout<<"TextureMgr constructor"<<endl;}
~TextureMgr(){cout<<"TextureMgr destructor"<<endl;}
};
//TextureMgrGof
class TextureMgr_Gof:public TextureMgrBase, public Singleton_Gof<TextureMgr_Gof>{
public:
TextureMgr_Gof(){cout<<"TextureMgr_Gof constructor"<<endl;}
~TextureMgr_Gof(){cout<<"TextureMgr_Gof destructor"<<endl;}
};
因爲加了斷言保證只有一次調用,所以就能全局唯一了,因此我們便可以如下來使用這紋理管理器(需要手動刪除):
//【main.cpp】
#include "TextureMgr.h"
#include<iostream>
using namespace std;
#define g_TexMgr TextureMgr::getSingleton()
#define g_TexMgr_Gof TextureMgr_Gof::getSingleton()
int main(char argc, char* argv[])
{
//TextureMgr
Texture* tex1 = g_TexMgr.getTexture("紋理1");
Texture* tex2 = g_TexMgr.getTexture("紋理2");
Texture* _tex1 = g_TexMgr.getTexture("紋理1");
cout<<tex1->getName()<<endl;
cout<<tex2->getName()<<endl;
cout<<_tex1->getName()<<endl;
tex1->doSomeThing();
tex2->doSomeThing();
_tex1->doSomeThing();
delete &g_TexMgr;
cout<<endl;
//TextureMgr_Gof
Texture* tex3 = g_TexMgr_Gof.getTexture("紋理3");
Texture* tex4 = g_TexMgr_Gof.getTexture("紋理4");
Texture* _tex3 = g_TexMgr_Gof.getTexture("紋理3");
cout<<tex3->getName()<<endl;
cout<<tex4->getName()<<endl;
cout<<_tex3->getName()<<endl;
tex1->doSomeThing();
tex2->doSomeThing();
_tex3->doSomeThing();
delete &g_TexMgr_Gof;
system("pause");
return 0;
}
得到的最終結果如下: