在其他类别中声明的私人成员

Question

I'm programming my first big "class" in a c++ program (it deals with I/O stream) and I think I understood the concepts of object, methods and attributes. Though I guess I still don't get all the rights of the encapsulation notion, because I want my class called File to have

• a name (the path of the file),
• a reading stream, and
• a writing stream

as attributes,

and also its first method to actually get the "writing stream" attribute of the File object...

#include <string>
#include <fstream>

class File {
public:
    File(const char path[]) : m_filePath(path) {}; // Constructor
    File(std::string path) : m_filePath(path) {}; // Constructor overloaded
    ~File(); // Destructor
    static std::ofstream getOfstream(){ // will get the private parameter std::ofStream of the object File
        return m_fileOStream;
    };
private:
    std::string m_filePath; // const char *m_filePath[]
    std::ofstream m_fileOStream;
    std::ifstream m_fileIStream;
};

But I get the error:

Error 4 error C2248: 'std::basic_ios<_Elem,_Traits>::basic_ios' : cannot access private member declared in class 'std::basic_ios<_Elem,_Traits>' c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\fstream 1116

reporting me to the following part of fstream.cc :

private:
    _Myfb _Filebuffer;  // the file buffer
    };

Could you then help me to fix this and be able to use a stream as parameter of my class please? I have tried to return a reference instead of the stream itself, but I'm gonna need some help with that as well (doesn't work either...). Thanks in advance

Answer 1

change

static std::ofstream getOfstream(){ // will get the private parameter std::ofStream of the object File
        return m_fileOStream;
    };

to

// remove static and make instance method returning a reference
// to avoid the copy constructor call of std::ofstream
std::ostream& getOfstream(){ return m_fileOStream; }

Answer 2

Each class has three section, So suppose the following class:

class Example{

public:
   void setTime(int time);
   int getTime() const;
private:
 int time;
protected:
bool ourAttrib;

}

You see public, private and protected words, yes, They explain encapsulation , When you can use private for method or attributes, just members can use it.But when you use public, everbody use it.Now protected: when you a class derived from this class, derived class can use protected and inherited them.