C++ 如何使操作员过载<&书信电报；对于使用共享基类的派生类？

我正在尝试重载

操作符
只有
virtual
函数允许根据对象的动态类型（给定基类的静态类型）进行调度


只有非静态成员函数才能
虚拟


运算符您不能覆盖
operator@Till它（查看
问题
中的decl）向我们展示了打印方法和术语的实现：重载意味着拥有两个同时可访问的同名函数，以及基于参数类型的自动编译时选择。重写意味着拥有一组具有相同参数类型的函数，其中一个由“acting”对象的动态类型选择。我有一个经常被过度使用的水晶球，它告诉我，在将派生类型发送到输出迭代器之前，您正在将其对象切片到
问题。你能把插入操作符的代码和你对它的实际用法贴出来吗？“漂亮吗？”波塔托斯沃特：我想你把这个问题弄得比以前更不正确了。您不能覆盖
class Question {
public:
    enum Type{TEXT, CHOICE, BOOL, SCALE};
    Question():
        type_(), question_() {}
    Question(Type type, std::string question):
        type_(type), question_(question) {}
    friend std::ostream& operator<<(std::ostream& out, const Question& q);
    virtual void print(std::ostream& out) const;
    virtual ~Question();
    private:
    Type type_;
    std::string question_;
};

class TextQuestion: public Question {
public:
    TextQuestion():
        Question() {}
    TextQuestion(Type type, std::string question):
        Question(type, question) {}
    void print(std::ostream& out) const;
    virtual ~TextQuestion();
};

class ChoiceQuestion: public Question {
public:
    ChoiceQuestion():
        Question(), choices_() {}
    ChoiceQuestion(Type type, std::string question, std::vector<std::string> choices):
        Question(type, question), choices_(choices) {}
    void print(std::ostream& out) const;
    virtual ~ChoiceQuestion();
private:
    std::vector<std::string> choices_;
};

class BoolQuestion: public Question {
public:
    BoolQuestion():
        Question() {}
    BoolQuestion(Type type, std::string question):
        Question(type, question) {}
    void print(std::ostream& out) const;
    virtual ~BoolQuestion();
};

class ScaleQuestion: public Question {
public:
    ScaleQuestion():
        Question(), low_(), high_() {}
    ScaleQuestion(Type type, std::string question, int low = 0, int high = 0):
        Question(type, question), low_(low), high_(high) {}
    void print(std::ostream& out) const;
    virtual ~ScaleQuestion();
private:
    int low_, high_;
};

std::ostream& operator<<(std::ostream& out, const Question& q) {
q.print(out);
return out;
}

void Question::print(std::ostream& out) const {
    std::string type;
    switch(type_) {
    case Question::TEXT:
        type = "TEXT";
        break;
    case Question::CHOICE:
        type = "CHOICE";
        break;
    case Question::BOOL:
        type = "BOOL";
        break;
    case Question::SCALE:
        type = "SCALE";
        break;
    }
    out << type << " " << question_;
}

void TextQuestion::print(std::ostream& out) const {
    Question::print(out);
}

void ChoiceQuestion::print(std::ostream& out) const {
    Question::print(out);
    out << std::endl;
    int size(get_choices_size());
    for (int i = 0; i < size; ++i) {
        out << choices_[i] << std::endl;
    }
}

void BoolQuestion::print(std::ostream& out) const {
    Question::print(out);
   }

void ScaleQuestion::print(std::ostream& out) const {
    Question::print(out);
        out << " " << low_ << " " << high_;
}  

TextQuestion q( "What is hello, world?" ); // Original object
Question & qr( q ); // Reference, not another object
Question q2( q ); // Base class object with copied subset (slice) of data.

std::cout << q << '\n'; // Observe subclass behavior.
std::cout << qr << '\n'; // Observe subclass behavior due to dynamic typing.
std::cout << q2 << '\n'; // Observe superclass behavior due to slicing.