如何创建模板化类对象的数组? [英] How to create an array of templated class objects?

问题描述

我已经有很长一段时间没有做过任何 C++ 编程了，我决定在我的业余时间稍微弄点它，所以我决定写一个小数据库程序只是为了好玩，我有创建模板化类对象数组时遇到问题.

I haven't done any C++ programming for quite some time and I decided that I would mess around with it a little bit in my spare time so I decided to write me a little database program just for fun and I'm having trouble with creating an array of templated class objects.

我拥有的是这个类，我想用它来表示数据库记录中的一个字段.

What I have is this class which I want to use to represent a field in a database record.

template <class T, int fieldTypeId>
class Field
{
private:
    T field;
    int field_type;
public:
    // ...
};

并且我想使用该类的数组来表示使用该类的数据库中的记录.

And I want to use an array of that class to represent a record in a database using this class.

class Database_Record
{
private:
    int id;
    Field record[];
public:
    Database_Record(int);
    Database_Record(int, Field[]);
   ~Database_Record();
};

我遇到的问题是在 Database_Record 类中创建数组，因为这是一个模板化类对象的数组，每个元素可能是不同的类型，我不确定因此我需要如何声明数组.我正在尝试做的事情是可能的还是我以错误的方式去做?任何帮助将不胜感激.

Where I'm stuck at is the creation of the array in the Database_Record class since that is an array of templated class objects with each element possibly being of a different type and I'm not sure how I need declare the array because of that. Is what I'm trying to do even possible or am I going about it the wrong way? Any help would be greatly appreciated.

推荐答案

Field 和 Field 是两种完全不同的类型.要在向量中处理它们，您需要在某处进行泛化.你可以写 AbstractField 和

Field<T1> and Field<T2> are two completely different types. To treat them in a vector you need to generialize then somewhere. You may write AbstractField and

struct AbstractField{
  virtual ~AbstractField() = 0;
};

template<class T,int fieldTypeId>
class Field: public AbstractField{
  private:
    T field;
  public:
    const static int field_type;
  public:
    virtual ~Field(){}
};

class Database_Record{
  std::vector<AbstractField*> record; 
  public:
    ~Database_Record(){
      //delete all AbstractFields in vector
    }
};

然后保留一个AbstractField的vector.也使用 vector 而不是 [].使用 AbstractField* 而不是 AbstractField 并在 AbstractField 中至少写一个纯虚拟.

and then keep a vector of AbstractField. also use vector instead of []. Use AbstractField* instead of AbstractField and write at least one pure virtual in AbstractField.

您可以将 AbstractField 的析构函数设为纯虚拟.并且不要忘记删除所有 AbstractFields.在 ~Database_Record()

you may make the destructor of AbstractField pure virtual. and don't forget to delete all AbstractFields. in ~Database_Record()

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