C++: Why does my DerivedClass's constructor not have access to the BaseClass's protected field?

Question

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() { } 

//The compiler error

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

Any help is greatly appreciated. Thank you in advance.

Answer 1

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

That is: DerivedClass::DerivedClass(std::string data) : BaseClass(data) { }