抽象类的 QDataStream 运算符<<重载

Question

我想超载＆lt;＆lt;＆lt; atraft class class 作为虚拟操作员，我知道如何超载操作员的运算符下面的简单类和代码是一个示例。

  class NormalClass
    {
    public:
        int firstField() const;
        void setFirstField(int firstField);
        int secondField() const;
        void setSecondField(int secondField);
    private:
        int m_firstField;
        int m_secondField;
    };
    QDataStream &operator<<(QDataStream &out, const NormalClass &obj)
    {
        out << obj.firstField();
        out << obj.secondField();
        return out;
    }

但是现在，假设我们有摘要baseclass，如下

class AbstractBaseClass
{
public:
    AbstractBaseClass() {}
    int BaseFirstField() const;
    void setBaseFirstField(int BaseFirstField);
    int BaseSecondField() const;
    void setBaseSecondField(int BaseSecondField);
private :
    int m_BaseFirstField;
    int m_BaseSecondField;
};

class ChildClass : public AbstractBaseClass
{
public:
    ChildClass() {}

    int ChildFirstField() const;
    void setChildFirstField(int ChildFirstField);
private:
    int m_ChildFirstField;
}

现在我想超载＆lt;＆lt;摘要baseclass的操作员应该实施哪个孩子。

这是我的尝试

#ifndef ABSTRACTBASECLASS_H
#define ABSTRACTBASECLASS_H
#include <QDataStream>
class AbstractBaseClass
{
public:
    AbstractBaseClass();
    int BaseFirstField() const;
    void setBaseFirstField(int BaseFirstField);
    int BaseSecondField() const;
    void setBaseSecondField(int BaseSecondField);
private :
    int m_BaseFirstField;
    int m_BaseSecondField;
};
virtual QDataStream &operator<<(QDataStream &out, const AbstractBaseClass &obj)=0;

#endif // ABSTRACTBASECLASS_H

编译器抱怨：虚拟外部班级声明，您有任何想法吗？

Answer 1

我尝试并成功编译的内容，您如何看待此方法，并且有更好的成就。

这是抽象类

.h

#ifndef ABSTRACTBASECLASS_H
#define ABSTRACTBASECLASS_H
#include <QDataStream>
class AbstractBaseClass
{
public:
    AbstractBaseClass();
    int BaseFirstField() const;
    void setBaseFirstField(int BaseFirstField);
    int BaseSecondField() const;
    void setBaseSecondField(int BaseSecondField);
    virtual QDataStream &serialize(QDataStream &stream)=0;
private :
    int m_BaseFirstField;
    int m_BaseSecondField;
};
QDataStream &operator<<(QDataStream &out, AbstractBaseClass &obj);
#endif // ABSTRACTBASECLASS_H

.cpp

 #include "abstractbaseclass.h"
AbstractBaseClass::AbstractBaseClass()
{
    m_BaseFirstField = 0;
    m_BaseSecondField = 0;
}
int AbstractBaseClass::BaseFirstField() const
{
    return m_BaseFirstField;
}
void AbstractBaseClass::setBaseFirstField(int BaseFirstField)
{
    m_BaseFirstField = BaseFirstField;
}
int AbstractBaseClass::BaseSecondField() const
{
    return m_BaseSecondField;
}
void AbstractBaseClass::setBaseSecondField(int BaseSecondField)
{
    m_BaseSecondField = BaseSecondField;
}

QDataStream &operator<<(QDataStream &out, AbstractBaseClass &obj)
{
    return obj.serialize(out);
}

和儿童课

class ChildClass : public AbstractBaseClass
{
public:
    ChildClass(){}
    int ChildFirstField() const
    {
        return m_ChildFirstField;
    }
    void setChildFirstField(int ChildFirstField)
    {
        m_ChildFirstField = ChildFirstField;
    }
private:
    int m_ChildFirstField;
    // AbstractBaseClass interface
public:
    QDataStream &serialize(QDataStream &stream) override
    {
        stream << BaseFirstField();
        stream << BaseSecondField();
        stream << ChildFirstField();
        return stream;
    }
};