非虚接口-如何调用正确的虚函数

Question

我有一个层次结构，看起来像这样:

class Base
{
public:
    void Execute();
    virtual void DoSomething() = 0;
private:
    virtual void exec_();
};
class Derived : public Base
{
public:
   //DoSomething is implementation specific for classes Derived from Base
   void DoSomething();
private:
    void exec_();
};
void Base::Execute()
{
    // do some work 
    exec_();  //work specific for derived impl
    // do some other work
}
void Derived::DoSomething()
{
   //impl dependent so it can only be virtual in Base
}

int main()
{
  Derived d;
  Base& b = d;
  b.Execute();  //linker error cause Derived has no Execute() function??
}

所以问题是，当我使用基类创建派生时，我如何使用这种模式调用Execute()。在我的例子中，我不想直接创建派生类，因为我有多个从Base派生的类，并且根据某些条件，我必须选择一个不同的派生类。

有人能帮忙吗?

Answer 1

This

class Base
{
public:
    void Execute();
private:
    virtual void exec_() {}
};
class Derived : public Base
{
private:
    void exec_() {}
};
void Base::Execute()
{
    // do some work 
    exec_();  //work specific for derived impl
    // do some other work
}
int main()
{
    Derived d;
    Base& b = d;
    b.Execute();
}

为我编译、链接和运行。

Answer 2

您可能还应该在基类中将exec_()设置为纯虚的。然后，您还需要在派生类中实现它。

Answer 3

您需要为exec_()函数编写一个函数定义