如何使用带向量和共享指针的派生类？ [英] How shall I use derived classes with vectors and shared pointers?

问题描述

我不熟悉继承的概念，我很难找到解决以下问题的方法。

I am not familiar with the concept of inheritance, and I am struggling to find a solution to the following problem.

我有2个班，头和手。我主要使用这些类的实例作为向量的元素。这两个类有共同的方法和只有它们特有的方法。

I have 2 classes, Head and Hand. I use instances of these classes mostly as elements of a vector. The two classes have methods in common and methods peculiar only to them.

此外，我处理对象的共享指针。

Moreover, I deal with shared pointers of the object.

我认为实现它的最佳方法是创建一个类BodyPart，就像这样

I thought the best way to implement it was to create a class BodyPart, like this

class BodyPart
{
  public:
  typedef boost::shared_ptr<BodyPart> pointer;

  private:
  int commonMember1;
  double commonMember2;

  public:
  int commonMethod1();
  int CommonMethod2();
}

以及这样的两个派生类

class Hand : public BodyPart
{
  public:
  typedef boost::shared_ptr<Hand> pointer;

  private:
  int numFingers;

  public:
  int getNumFingers();
  void printInfo();
}

最后，我想声明一个BodyPart元素的向量：

Finally, I wanted to declare a vector of BodyPart elements:

std::vector<BodyPart::pointer> cBodyParts;

包含Hand或Head元素，并在需要时在vector元素上调用我的方法。

containing either Hand or Head elements, and call my methods on the vector elements when I need.

但这种方法似乎效果不佳。显然，当我尝试获取向量的元素时，编译器会抱怨它无法从BodyPart共享指针转换为Hand共享指针。此外，如果向量声明如上所述，我不能在其元素上调用特定于派生类的方法（如getNumFinger（）），即使实际上是来自该类。

But this approach doesn't seem to work very well. Apparently, when I try to get an element of the vector, the compiler complains that it cannot convert from a BodyPart shared pointer to a Hand shared pointer. Moreover, if the vector is declared like above, I cannot call methods specific to the derived classes (like getNumFinger() ) on its element, even if the actually are from that class.

有没有正确的方法来解决这个问题？或者我的方法完全错了？
提前致谢！

Is there a proper way to deal with this? Or is my approach completely wrong? Thanks in advance!

推荐答案

您的方法是正确的，但编译器也是如此。你有一个基类的共享指针向量，这很好，但你需要转换为实际类型才能获得特定的功能。

Your approach is correct, but so is the compiler. It's good that you have a vector of shared pointers to the base class, but you'll need to cast to the actual type to get specific functionality.

typedef boost :: shared_ptr< Hand>指针; 没用，你只需要基类中的 typedef 。你不会在智能指针之间进行投射。我将基类typedef重命名为

The typedef boost::shared_ptr<Hand> pointer; is useless though, you only need the typedef in the base class. You won't be casting between smart pointers. I'd rename the base class typedef to

typedef boost::shared_ptr<BodyPart> BodyPartPtr;

尽管如此。

Alan在评论中提出了很好的观点：你应该让基类的析构函数虚拟化以防止UB，因为你将通过a删除（间接）指向派生类型的指针指向基本类型的指针。

Good point by Alan in the comments: you should make the base class's destructor virtual to prevent UB, since you'll be deleting (indirectly) pointers to derived types through a pointer to a base type.

这篇关于如何使用带向量和共享指针的派生类？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！