制作一个地图，其中值类型是C ++中的抽象类

问题描述

我有一个抽象类element和一个子类elasticFrame:

I have an abstract class element and a child class elasticFrame :

class element
{
public:
    virtual Matrix getStiffness() = 0;
protected:
    Matrix K;
};


class elasticFrame3d:public element
{
public:
    elasticFrame3d(double E, double G);
    virtual Matrix getStiffness();
virtual Matrix getTransform();
private:
    double E, G;
};

我想要做的是这样的地图:

what I want is to make a map like this:

map<int, element> elementMap;

但是当我收到此错误时:

but when I get this error:

error C2259: 'element' : cannot instantiate abstract class

是否有可能做到这一点?如果是，怎么办?

is it even possible to do this? if yes how?

推荐答案

您将无法创建类型为element的值，因为它具有抽象功能.如果要存储从element派生的类型的对象，则需要存储合适的指针或对这些对象的引用.例如，您可以使用std::unique_ptr<element>或std::shared_ptr<element>(您需要包含#include <memory>)并将具体对象分配到合适的存储区域中.

You won't be able to create a value of type element as it has abstract function. If you want to store objects of a type derived from element, you'll need to store a suitable pointer or reference to these objects. You can, e.g., use std::unique_ptr<element> or std::shared_ptr<element> (you need to include #include <memory>) and allocate the concrete objects in a suitable memory area.

也就是说，您将使用以下内容:

That is, you would use something like this:

std::map<int, std::unique_ptr<element>> elementMap;
elementMap[17] = std::unique_ptr<element>(new elasticFrame3D(3.14, 2.71));

顺便说一句，您使用的是一个不常用的命名约定:使用CamelCase时，类型通常使用大写字母，而对象则使用小写首字母.

BTW, you are using an unusal naming convention: when using CamelCase types are normally written with a capital letter and objects using a lowercase initial letter.

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