问题
Any help is appriciated. I'm working on a C++ factory pattern and i get this error.
1>c:\users\brian\documents\visual studio 2010\projects\cst276lab_3\guitar.hpp(456): error C2259: 'ElectricGuitarComponentFactory' : cannot instantiate abstract class
This is my code:
///////////////////////guitar class////////////////////
class Guitar
{
private: std::string _name;
protected: mutable std::auto_ptr< HeadStock > _HeadStock;
protected: mutable std::auto_ptr< NeckStrap > _NeckStrap;
protected: mutable std::vector< Bridge* > _Bridge;
protected: mutable std::auto_ptr< Strings > _Strings;
protected: mutable std::auto_ptr< Switches > _Switches;
protected: mutable std::auto_ptr< GuitarBody > _GuitarBody;
public: virtual void prepare() const = 0;
private: Guitar( const Guitar& ); // Disable copy constructor
private: void operator=( const Guitar& ); // Disable assignment operator
protected: Guitar()
{
}
public: virtual ~Guitar()
{
for( std::vector< Bridge* >::iterator iterator = _Bridge.begin();
_Bridge.end() != iterator; ++iterator )
{
delete *iterator;
}
_Bridge.clear();
}
public: virtual void bake() const
{
std::cout << "Bake for 25 minutes at 350" << std::endl;
}
public: virtual void cut() const
{
std::cout << "Cutting the pizza into diagonal slices" << std::endl;
}
public: virtual void box() const
{
std::cout << "Place pizza in official PizzaStore box" << std::endl;
}
public: void setName( std::string name)
{
_name = name;
}
public: std::string getName() const
{
return _name;
}
public: std::string toString() const
{
std::stringstream value;
value << "---- " << _name.c_str() << " ----" << std::endl;
if( _HeadStock.get() != 0 )
{
value << _HeadStock->toString();
value << std::endl;
}
if( _NeckStrap.get() != 0 )
{
value << _NeckStrap->toString();
value << std::endl;
}
if( _Strings.get() != 0 )
{
value << _Strings->toString();
value << std::endl;
}
if( _GuitarBody.get() != 0 )
{
value << _GuitarBody->toString();
value << std::endl;
}
if( _Switches.get() != 0 )
{
value << _Switches->toString();
value << std::endl;
}
if( _Bridge.size() != 0 )
{
for( std::vector< Bridge* >::iterator iterator = _Bridge.begin();
_Bridge.end () != iterator; ++iterator )
{
value << ( *iterator )->toString() << ", ";
}
value << std::endl;
}
return value.str();
}
};
//////////////////////////////////////Class guitar store////////////////
class GuitarStore
{
protected: GuitarStore()
{
}
public: virtual ~GuitarStore() = 0
{
}
public: std::auto_ptr< Guitar > orderGuitar( std::string type ) const
{
std::auto_ptr< Guitar > guitar( createGuitar( type ) );
std::cout << "--- Making a " << guitar->getName() << " ---" << std::endl;
guitar->prepare();
guitar->bake();
guitar->cut();
guitar->box();
return guitar;
}
public: virtual std::auto_ptr< Guitar > createGuitar( std::string type ) const = 0;
};
//////////////////////////////////guitar component factory////////////////////////////////
class GuitarComponentFactory
{
public: virtual HeadStock* createHeadStock() const = 0;
public: virtual NeckStrap* createNeckStrap() const = 0;
public: virtual Strings* createStrings() const = 0;
public: virtual std::vector< Bridge* > createBridge() const = 0;
public: virtual Switches* createSwitches() const = 0;
public: virtual GuitarBody* createGuitarBody() const = 0;
public: virtual ~GuitarComponentFactory() = 0 {}
};
///////////////////////////// electric guitar///////////////////
class ElectricGuitar : public Guitar
{
private: mutable std::auto_ptr< GuitarComponentFactory > _ingredientFactory;
public: explicit ElectricGuitar( GuitarComponentFactory* ingredientFactory ) :
_ingredientFactory( ingredientFactory )
{
assert( ingredientFactory );
}
public: void prepare() const
{
std::cout << "Preparing " << getName().c_str() << std::endl;
_HeadStock = std::auto_ptr< HeadStock>( _ingredientFactory->createHeadStock() );
_NeckStrap = std::auto_ptr< NeckStrap>( _ingredientFactory->createNeckStrap() );
_Strings = std::auto_ptr< Strings>( _ingredientFactory->createStrings() );
_Switches= std::auto_ptr< Switches>( _ingredientFactory->createSwitches() );
if( _Bridge.empty() )
_Bridge = _ingredientFactory->createBridge();
}
};
//////////// electric guitar component factory////////////////
class ElectricGuitarComponentFactory : public GuitarComponentFactory
{
public: HeadStock* createHeadStock() const
{
return new AngledHeadStock();
}
public: NeckStrap* createNeckStrap() const
{
return new LeatherNeckStrap();
}
public: Strings* createStrings() const
{
return new NylonStrings();
}
public: std::vector< Bridge* > createBridge() const
{
std::vector< Bridge* > bridge;
bridge.push_back( new ChromeBridge() );
return bridge;
}
public: Switches* createSwithes() const
{
return new SPDT_Switches();
}
public: GuitarBody* createGuitarBody() const
{
return new HollowGuitarBody();
}
};
//////////////////// electric guitar srore ////////////////
class ElectricGuitarStore : public GuitarStore
{
public: std::auto_ptr< Guitar > createGuitar( std::string item ) const
{
std::auto_ptr< Guitar > guitar( 0 );
GuitarComponentFactory* ingredientFactory = new ElectricGuitarComponentFactory();
if( item.compare( "Electric" ) == 0 )
{
guitar = std::auto_ptr< Guitar >( new ElectricGuitar( ingredientFactory ) );
guitar->setName( "Electric GuitarBody" );
return guitar;
}
}
};
any help would be nice thanks ahead of time...=)
回答1:
To fix the specific problem, you need to declare a destructor for ElectricGuitarComponentFactory because you have declared the destructor of the base class as a pure virtual function. Why you have declared the base class destructor as pure virtual, I don't know; it really doesn't make any sense to do that. The destructor should be declared virtual, but not as pure virtual.
Also, the syntax you have used,
public: virtual ~GuitarComponentFactory() = 0 {}
is ill-formed. You cannot declare a pure virtual function and provide a definition for it in the class definition. If you want to provide a definition for a pure virtual function, you must do so outside of the class definition. The compiler you are using, Visual C++, is a bit lenient with respect to this rule.
回答2:
class GuitarComponentFactory
{
public: virtual ~GuitarComponentFactory() = 0 {}
};
In your derived ElectricGuitarComponentFactory you don't provide a destructor, hence it's still an abstract class.
回答3:
ElectricGuitarComponentFactory inherits GuitarComponentFactory ....
When you inherit an abstract class (abstract = has pure virtual methods), then you need to override all those methods.
in GuitarComponentFactory you got 7 methods, and in ElectricGuitarComponentFactory you only declared 6.
You forgot to override the destructor.
来源：https://stackoverflow.com/questions/4989480/why-did-i-get-the-error-error-c2259-cannot-instantiate-abstract-class