将基本类的对象扩展到复杂类的对象

Question

我怎样才能做到这一点？我想到了复杂类中的一种方法，它将基本对象的每个变量复制到复杂对象，但这似乎有点不方便。

class Basic
{
  //basic stuff
}

class Complex : public Basic
{
  //more stuff
}

Basic * basicObject = new Basic();
//now "extending" basicObject and "cast" it to Complex type
//which means copy everything in basicObject to an complexObject

或者类似的东西：

Complex * complexObject = new Complex();
complexObject.getEverythingFrom(basicObject);

似乎太不方便了，因为每次我更改Basic类时，我也必须更改这个“复制”方法。

Answer 1

定义要在受保护部分中的类之间共享的值，如下所示：

class Base
{
public:
int myPublicShared1;
int myPublicShared2;

Base& operator = (Base& other)
{
    // Copy contents in base across
    return *this;
}
protected:
int myShared1;
int myShared2;

private:
int notShared1;
int notShared2;
};

class Derived : public Base
{
public:
Derived& operator = (Derived& other)
{
    Base::operator = (other);
    // copy the rest of variables specific to Derived class.
}
Derived& operator = (Base& other)
{
    Base::operator = (other);
}
// Derived now has all variables declared in Base's public and protected section
};

Answer 2

在 C++ 中，对象不能更改其类型。

因此，要么重写程序以立即创建 Complex 对象，要么创建一个复制构造函数，以便可以执行以下操作：

new Complex(*basicObject);

旁注：从像extend这样的词和new的用法来看，你似乎来自java世界。不要错误地认为在 Java 中做事的方式也是在 C++ 中做事的方式。