抽象类的C ++工厂方法模式(C++ factory method pattern for abstract class)

 我必须在C ++中实现工厂方法模式。 由工厂“组装”的类（C）是抽象的，并由其他类（D）继承。 所以我不想C有一个构造函数。 但是为了创建一个D的实例，C必须至少有一个受保护的构造函数。 但是，有人可能从C派生出来，并以这种方式创建C的一个实例。 我不希望发生这种情况。 所以我创建了一个受保护的构造函数，它接受一个指向C对象的指针以供派生类使用，代码如下所示。 问题是这是否是解决这个问题的正确方法。 
 
class C {
private:
 C() {}
protected:
 C(const C* c) {}
friend class CFactory
};

class D: public C
{
private:
 D(const C* c): C(c) {}
friend class CFactory;
};

class CFactory
{
public:
 static C* createC() {
  C* ptr = new C();
  ptr = new D(ptr); // There is garbage collection on the project, so no memory leak.
 }
};

I have to implement a factory method pattern in C++. The class (C) that is to be "assembled" by the factory is abstract and is inherited by some other class (D). So I don't want C to have a constructor. But to create an instance of D, C has to have at least a protected constructor. But then someone might derive from C and create an instance of C in this way. I don't want this to happen. So I created a protected constructor that takes a pointer to a C object for derived classes to use, code is below. The question is whether that is the correct way of dealing with this issue.
 
class C {
private:
 C() {}
protected:
 C(const C* c) {}
friend class CFactory
};

class D: public C
{
private:
 D(const C* c): C(c) {}
friend class CFactory;
};

class CFactory
{
public:
 static C* createC() {
  C* ptr = new C();
  ptr = new D(ptr); // There is garbage collection on the project, so no memory leak.
 }
};

原文：https://stackoverflow.com/questions/6295248