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CBase* pBase(NULL);
switch (type_variable)
{
case obj1: pBase = new CBaseDerivate1();break;
case obj2: pBase = new CBaseDerivate2();break;
...
case objN: pBase = new CBaseDerivateN();break;
}CBase* pBase(NULL);
if (!strcmp(string_for_type, "Type1")) pBase = new CBaseDerivate1();
else if (!strcmp(string_for_type, "Type2")) pBase = new CBaseDerivate2();
...
else if (!strcmp(string_for_type, "TypeN")) pBase = new CBaseDerivateN();上面两中创建对象的方法使用起来很繁琐，并且当对象的数量增加时，维护起来很麻烦，下面介绍简单工厂模式来解决该问，采用两种方法实现，一种是采用注册函数指针，另外一种采用模板参数。class IAnimal
{
public:
virtual int GetNumberOfLegs() const = 0;
virtual void Speak() = 0;
virtual void Free() = 0;
}; 2.定义具体的动物实例// IAnimal implementations
class Cat : public IAnimal
{
public:
int GetNumberOfLegs() const { return 4; }
void Speak() { cout << “Meow” << endl; }
void Free() { delete this; }
static IAnimal * __stdcall Create() { return new Cat(); }
};
class Dog : public IAnimal
{
public:
int GetNumberOfLegs() const { return 4; }
void Speak() { cout << “Woof” << endl; }
void Free() { delete this; }
static IAnimal * __stdcall Create() { return new Dog(); }
};
class Spider : public IAnimal // Yeah it isn’t really an animal…
{
public:
int GetNumberOfLegs() const { return 8; }
void Speak() { cout << endl; }
void Free() { delete this; }
static IAnimal * __stdcall Create() { return new Spider(); }
};
class Horse : public IAnimal
{
public:
int GetNumberOfLegs() const { return 4; }
void Speak() { cout << “A horse is a horse, of course, of course.” << endl; }
void Free() { delete this; }
static IAnimal * __stdcall Create() { return new Horse(); }
};typedef IAnimal* (__stdcall *CreateAnimalFn)(void);
// Factory for creating instances of IAnimal
class AnimalFactory
{
private:
AnimalFactory();
AnimalFactory(const AnimalFactory &) { }
AnimalFactory &operator=(const AnimalFactory &) { return *this; }
typedef map FactoryMap;
FactoryMap m_FactoryMap;
public:
~AnimalFactory() { m_FactoryMap.clear(); }
static AnimalFactory *Get()
{
static AnimalFactory instance;
return &instance;
}
void Register(const string &animalName, CreateAnimalFn pfnCreate);
IAnimal *CreateAnimal(const string &animalName);
};构造函数进行具体创建函数的注册/* Animal factory constructor.
Register the types of animals here.
*/
AnimalFactory::AnimalFactory()
{
Register(“Horse”, &Horse::Create);
Register(“Cat”, &Cat::Create);
Register(“Dog”, &Dog::Create);
Register(“Spider”, &Spider::Create);
}
void AnimalFactory::Register(const string &animalName, CreateAnimalFn pfnCreate)
{
m_FactoryMap[animalName] = pfnCreate;
}IAnimal *AnimalFactory::CreateAnimal(const string &animalName)
{
FactoryMap::iterator it = m_FactoryMap.find(animalName);
if( it != m_FactoryMap.end() )
return it->second();
return NULL;
}int main( int argc, char **argv )
{
IAnimal *pAnimal = NULL;
string animalName;
while( pAnimal == NULL )
{
cout << “Type the name of an animal or ‘q’ to quit: “;
cin >> animalName;
if( animalName == “q” )
break;
IAnimal *pAnimal = AnimalFactory::Get()->CreateAnimal(animalName);
if( pAnimal )
{
cout << “Your animal has ” << pAnimal->GetNumberOfLegs() << ” legs.” << endl;
cout << “Your animal says: “;
pAnimal->Speak();
}
else
{
cout << “That animal doesn’t exist in the farm! Choose another!” << endl;
}
if( pAnimal )
pAnimal->Free();
pAnimal = NULL;
animalName.clear();
}
return 0;
}template <class BT>
class FactoryPlant
{
public:
FactoryPlant() {}
virtual ~FactoryPlant() {}
virtual BT *createInstance() = 0;
};
template <class BT,class ST>
class Factory : public FactoryPlant<BT>
{
public:
Factory() {}
virtual ~Factory() {}
virtual BT *createInstance() {return new ST;}
};FactoryPlant
包含创建实例的纯虚函数createInstance,子类Factory实现该方法。
2.创建具体子类 //抽象动物接口class IAnimal
{
public:
virtual int GetNumberOfLegs() const = 0;
virtual void Speak() = 0;
virtual void Free() = 0;
typedef FactoryPlant<IAnimal> SimpleBaseClassFactory;
};
class Cat : public IAnimal
{
public:
int GetNumberOfLegs() const { return 4; }
void Speak() { cout << "Meow" << endl; }
void Free() { delete this; }
static Factory<IAnimal,Cat> myFactory;
};
Factory<IAnimal,Cat> Cat::myFactory;
class Dog : public IAnimal
{
public:
int GetNumberOfLegs() const { return 4; }
void Speak() { cout << "Woof" << endl; }
void Free() { delete this; }
static Factory<IAnimal,Dog> myFactory;
};
Factory<IAnimal,Dog> Dog::myFactory;
class Spider : public IAnimal //
{
public:
int GetNumberOfLegs() const { return 8; }
void Speak() { }
void Free() { delete this; }
static Factory<IAnimal,Spider> myFactory;
};
Factory<IAnimal,Spider> Spider::myFactory;
class Horse : public IAnimal
{
public:
int GetNumberOfLegs() const { return 4; }
void Speak() { cout << "A horse is a horse, of course, of course." << endl; }
void Free() { delete this; }
static Factory<IAnimal,Horse> myFactory;
};
Factory<IAnimal,Horse> Horse::myFactory;
IAnimal *CreateAnimal(std::map<string,IAnimal::SimpleBaseClassFactory *> &factories,const string &animalName)
{
return factories[animalName]->createInstance();
}
4.客户端使用void main()
{
IAnimal *pAnimal = NULL;
//Register
std::map<string,IAnimal::SimpleBaseClassFactory *> factories;
factories["Cat"] = &Cat::myFactory;
factories["Dog"] = &Dog::myFactory;
factories["Spider"] = &Spider::myFactory;
factories["Horse"] = &Horse::myFactory;
string animalName;
while( pAnimal == NULL )
{
cout << "Type the name of an animal or 'q' to quit: ";
cin >> animalName;
if( animalName == "q" )
break;
IAnimal *pAnimal = CreateAnimal(factories,animalName);
if( pAnimal )
{
cout << "Your animal has " << pAnimal->GetNumberOfLegs() << " legs." << endl;
cout << "Your animal says: ";
pAnimal->Speak();
}
else
{
cout << "That animal doesn't exist in the farm! Choose another!" << endl;
}
if( pAnimal )
pAnimal->Free();
pAnimal = NULL;
animalName.clear();
}
原文：http://blog.csdn.net/xiaoding133/article/details/44995145