C++继承测验

Question

我最近被问到一个基本的C++问题,我实际上并不知道答案,我从来没有发现答案是什么.这是一个问题:

运行此程序时,可能会导致错误.您将对Base类进行哪些更改来修复它？

#include <iostream>

class Base {
public:
    virtual void ShowMessage () {
        std::cout << "Base class message\n";
    }

    // Something should be added here!
};

class Derived : public Base {
public:
    explicit Derived (const std::string & value)
        : myValue(value)
    {
    }

    virtual void ShowMessage () {
        std::cout << "Derived class message " << myValue << "\n";
    }

private:
    std::string myValue;
};

int main () {
    Base * obj = new Derived("Test message");
    obj->ShowMessage();
    delete obj;
}

它在我的机器上编译并运行得很好.有谁知道他们在找什么？

Answer 1

您需要向Base类添加虚拟析构函数.

class Base {
public:
    virtual void ShowMessage () {
        std::cout << "Base class message\n";
    }

    virtual ~Base() {}
};

在您的情况下,Derived :: myvalue将无法正确发布.