C ++：为什么我的DerivedClass的构造函数不能访问BaseClass的protected字段？ [英] C++: Why does my DerivedClass's constructor not have access to the BaseClass's protected field?

问题描述

我有一个构造函数尝试初始化基类中的字段。编译器抱怨。该字段受保护，因此派生类应该具有访问权。

I have a constructor attempting to initialize a field in a base class. The compiler complains. The field is protected, so derived classes should have access.

//The base class: 

class BaseClass

{

public:

    BaseClass(std::string);
    BaseClass(const BaseClass& orig);
    virtual ~BaseClass();
    const std::string GetData() const;
    void SetData(const std::string& data);
protected:

    BaseClass();
    std::string m_data;

};

BaseClass::BaseClass(const std::string data) : m_data(data) { }

BaseClass::BaseClass() { } 

BaseClass::BaseClass(const BaseClass& orig) { }

BaseClass::~BaseClass() { }

void BaseClass::SetData(const std::string& data)
{
    m_data = data;
}

const std::string BaseClass::GetData() const
{
    return m_data;
}


//The derived class: 


class DerivedClass : public BaseClass
{

public:

    DerivedClass(std::string data);
    DerivedClass(const DerivedClass& orig);
    virtual ~DerivedClass();
private:

};

DerivedClass::DerivedClass(std::string data) : m_data(data) { } //ERROR HERE

DerivedClass::DerivedClass(const DerivedClass& orig) { }

DerivedClass::~DerivedClass() { }

错误

DerivedClass.cpp：3：错误：类'DerivedClass'没有任何名为'm_data'的字段

DerivedClass.cpp:3: error: class ‘DerivedClass’ does not have any field named ‘m_data’

任何帮助是非常感谢。提前感谢。

Any help is greatly appreciated. Thank you in advance.

推荐答案

您不能在派生类构造函数中初始化m_data，而是将其作为参数传递给基类构造函数。

You cannot initialize m_data in the derived class constructor but instead pass it as an argument to the base class constructor.

这是： DerivedClass :: DerivedClass（s​​td :: string data）：BaseClass（data）{}

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