C ++抽象类继承虚拟函数

Question

我有一个抽象基类，其中包含一些属性或成员元素以及一些公共函数和公共纯虚函数。 在抽象类的派生类中，我想（a）以私有成员的身份访问抽象基类的成员，并且（b）公共函数和定义的纯虚函数保持为公共状态。 有办法吗？ 也就是说，派生类中的AbstractBase和yyyy访问说明符的xxxx应该是什么？

#include <iostream>

class AbstractBase {
 xxxx: <-- // protected/private/public?
  std::string baseprivate1;

 public:
  virtual void set_privates() = 0;
  void print() { std::cout << baseprivate1 << std::endl; }
  void foo() { // some definition here }
};

class Derived : yyyy AbstractBase {  <--- //public/protected/private? 
 private:
  std::string derivedprivate1;

 public:
  void set_privates() {
    // I want this baseprivate1 to be private in derived class as well.
    // When I choose xxxx as protected and yyyy as public, the baseprivate1 is protected. 
    this->baseprivate1 = "Base private1";
    this->derivedprivate1 = "Derived private1";
  }
  void print() {
    AbstractBase::print();
    std::cout << this->derivedprivate1;
  }
  // When I choose xxxx as protected and yyyy as protected
  // foo becomes protected and unable to call from outside
  // I want the foo of abstract base to be public here as well. 
};

int main(int argc, char *argv[]){
    Derived d;
    d.set_privates();
    d.print();
    d.foo(); // I should be able to call foo of abstract base class
}

可以将其混淆为私有继承，公共继承和受保护继承之间的差异的重复。 如果您将xxxx设置为受保护而yyyy设置为公共，则baseprivate1将在“派生”中受到保护，并且不再是私有的。 或者，如果xxxx为public / protected，而yyyy为private，则派生函数将变为private。

Answer 1

完成所需内容的一种方法是在Derived类上使用AbstractBase的私有继承。 然后，您可以在Derived类中的公共访问说明符下使用using声明来公开AbstractBase的一些方法。

#include <iostream>

class AbstractBase {
    public:
        std::string baseprivate1;

        virtual void set_privates() = 0;
        void print() { std::cout << baseprivate1 << std::endl; }
        void foo() { /* some definition here */ }
};

class Derived : private AbstractBase { // use private inheritance on AbstractBase
    private:
        std::string derivedprivate1;

    public:
        // expose AbstractBase's methods with using-declarations
        using AbstractBase::foo;
        using AbstractBase::print;

        void set_privates() {
            this->baseprivate1 = "Base private1";
            this->derivedprivate1 = "Derived private1";
        }

        void print() {
            AbstractBase::print();
            std::cout << this->derivedprivate1 << std::endl;;
        }
};

int main(int argc, char *argv[]){
    Derived d;
    d.set_privates();
    d.print();
    d.foo();
    return 0;
}