复制构造函数和基类C ++ [英] copy constructors and base classes C++

问题描述

我想能够从基类初始化一个派生类，例如：

I'd like to be able to initialize a derived class from a base class, like so:

class X {
   public:
   X() : m(3) {}
   int m;
};

class Y : public X {
   public: 
   Y() {}
   Y(const & X a)  : X(a) {}
};

有什么危险或不寻常的做法吗？我想要它，因为我反序列化一堆对象类型我不立即知道，所以我基本上想使用X作为一些临时存储，而我正在读整个序列化文件，然后创建我的Y对象和W，X，Yobjs，取决于数据）。

Is there anything dangerous or unusual by doing that? I want it because I'm deserializing a bunch of objects who's type I don't immediately know, so I basically want to use X just as some temp storage while I'm reading the whole serialized file, and then create my Y objects (and W, X, Y objs, depending on the data) using that data afterwards. Maybe there's a easier way I'm missing.

谢谢！

推荐答案

p>只要X有正确的拷贝ctor（自动生成或不生成），并设置 Y （如果有）的其他成员，

There should be no problem with this as long as X has a correct copy ctor (auto-generated or not) and you set the other members of Y (if any) to appropriate defaults.

我假设 Y 会有一些setter方法来更新 Y

I assume that Y would have some setter methods to update Y with the results of subsequent information from the serialization stream?

另请注意，您的 Y 从 X 构造函数应该有一个看起来更像的签名：

Also note that your Y from an X constructor should have a signature that looks more like:

Y( X const & a)   // the X was in an invalid place before

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