error C2248, what is this error and how do I fix it?

Question

I'm fairly new to c++ and currently trying to learn templates and how they work. My assignment asks me to create a parent class, base, that takes 4 arguments into a template. As well it must have a subclass that can print the values of the base class.

The parent class gets the values by reading a txt file.

Right now I'm trying to instantiate a subclass so that I can print the values line by line in the parent class.

My code is messy as I am VERY new to c++. My background consists of C#, Java and Javascript. Any help would be fantastic! Thanks in advance.

Error Message:

Error   1   error C2248: 'std::basic_ifstream<_Elem,_Traits>::basic_ifstream' : cannot access private member declared in class 'std::basic_ifstream<_Elem,_Traits>'

Code:

#include <iostream>
#include <string>
#include <fstream>
#include <sstream>
#include <iomanip>
#include <algorithm>
#include <cctype>

using namespace std;

//template that accept 4 different data types
template<class Type1, class Type2, class Type3, class Type4>
class Base {
    //protected declarations
    protected:
        Type1 str;
        Type2 i;
        Type3 d;
        Type4 b;

    //public declarations
    public:
        int lineRead;
        int data;
        string line, delimiter;
        size_t pos;
        ifstream inputfile;
        string token;

    //public functions
    public:
        void readFile(int lineNum) {
            //temp information holders
            lineRead = 0;
            pos = 0;
            delimiter = " ";

            //open .txt file
            inputfile.open("file.txt");

            //while end of file is not reached
            while (!inputfile.eof()) {
                //increment line counter
                lineRead++;

                //read line
                getline(inputfile,line);

                //if this is the line requested fill the template members with the
                //correct data. <string, int, double, bool>
                if(lineNum == lineRead){
                    //getting the string
                    pos = line.find(delimiter);
                    token = line.substr(0, pos);
                    str = token;
                    line.erase(0, pos + delimiter.length());

                    //getting the integer
                    pos = line.find(delimiter);
                    token = line.substr(0, pos);
                    i = stoi(token);
                    line.erase(0, pos + delimiter.length());

                    //getting the double
                    pos = line.find(delimiter);
                    token = line.substr(0, pos);
                    d = stod(token);
                    line.erase(0, pos + delimiter.length());

                    //getting the boolean
                    pos = line.find(delimiter);
                    token = line.substr(0, pos);
                    b = to_bool(token);
                    line.erase(0, pos + delimiter.length());
                }
            }

            //close the file
            inputfile.close();
            system("pause");
        };

        //Changes a string to lower case and then reads the string
        //to find if the value is true or false. Returns a boolean.
        bool to_bool(string str) {
            transform(str.begin(), str.end(), str.begin(), ::tolower);
            istringstream is(str);
            bool tempB;
            is >> boolalpha >> tempB;
            return tempB;
        }
};

class Subclass : public Base<string, int, double, bool> {
    private:
        string name;

    public:
        Subclass::Subclass(string name) {
            cout << "test";
        }

        void printValues() {
            cout << str;
        }


};

//main function
int main() {
    //call Base class and give the template data types
    Subclass b = Subclass("test");

    //read the file
    b.readFile(2);

    return 0;
}

score 1 · Accepted Answer · edited May 23 '17 at 11:59

1

Subclass b = Subclass("test");

This creates an object, and then tries to copy it. Your class is not copyable, hence the error (also, copying derived classes is problematic in its own way). To create an object without copying, use the following syntax:

Subclass b("test");

edited May 23 '17 at 11:59

Community

1
1

answered Apr 13 '16 at 16:37

anatolyg

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score 0 · Answer 2 · answered Apr 13 '16 at 16:34

You have an std::ifstream as a member, but they're non-copyable, hence hte error message you cited. Pre-C++11, the idiomatic way to make something non-copyable was to declare its copy constructor with a private access specifier (which is what you're seeing), so that nobody could accidentally use it. In C++11, the delete keyword is preferred and you'll get an error along the lines of "use of deleted function".

You should either:

Define a copy constructor and copy assignment operator
Not have a non-copyable member

I would go with (2) if I were you; ask yourself why you need this as a member and then find a way to factor it out.

error C2248, what is this error and how do I fix it?

2 Answers2