问C++向量发出“阻止匹配的限定符”

EN

void Exam:: read_questions(string filename) const{
    ifstream file;
    file.open(filename);
    if (file.is_open()){
        string line;
        while(getline(file,line)){
            Question* currentQuestion =  parse_question(line);
            question_list.push_back(currentQuestion);
        }
    }else{
        cout << "invalid file" << endl;
    }
    file.close();
}

class Exam 
{
public:
    Exam();
    Exam(int num_q, int min_chap, int max_chap);
    void read_questions(string filename) const;
    ~Exam();
    void write_exam(string filename) const;
    void write_key(string filename) const;
    void shuffle();

private:
    vector<Question *> question_list;
    int minC;
    int maxC;
    int numQ;
};