虚析构函数的作用？

虚析构函数在C++中的主要作用是用于解决基类指针指向派生类对象，并且通过基类指针删除对象时可能导致的内存泄漏问题。

当使用基类指针指向派生类对象，然后尝试删除该对象时，如果基类的析构函数不是虚的，只会调用基类的析构函数，而不会调用派生类的析构函数。

这可能导致派生类对象中的资源没有得到正确释放，从而产生内存泄漏。

通过将基类的析构函数声明为虚函数，就能够在基类指针指向派生类对象时正确地调用派生类的析构函数，确保对象的资源得到正确释放。

给个例子：

#include <iostream>
class Base {
public:
    Base() {
        std::cout << "Base constructor" << std::endl;
    }
    virtual ~Base() {
        std::cout << "Base destructor" << std::endl;
    }
};
class Derived : public Base {
public:
    Derived() {
        std::cout << "Derived constructor" << std::endl;
    }
    ~Derived() {
        std::cout << "Derived destructor" << std::endl;
    }
};
int main() {
    Base* obj = new Derived();
    delete obj;  // 正确释放资源，输出Derived destructor，然后输出Base destructor
    return 0;
}
#include <iostream>

class Base {
public:
    Base() {
        std::cout << "Base constructor" << std::endl;
    }

    virtual ~Base() {
        std::cout << "Base destructor" << std::endl;
    }
};

class Derived : public Base {
public:
    Derived() {
        std::cout << "Derived constructor" << std::endl;
    }

    ~Derived() {
        std::cout << "Derived destructor" << std::endl;
    }
};

int main() {
    Base* obj = new Derived();
    delete obj;  // 正确释放资源，输出Derived destructor，然后输出Base destructor

    return 0;
}
#include <iostream>

class Base {
public:
    Base() {
        std::cout << "Base constructor" << std::endl;
    }

    virtual ~Base() {
        std::cout << "Base destructor" << std::endl;
    }
};

class Derived : public Base {
public:
    Derived() {
        std::cout << "Derived constructor" << std::endl;
    }

    ~Derived() {
        std::cout << "Derived destructor" << std::endl;
    }
};

int main() {
    Base* obj = new Derived();
    delete obj;  // 正确释放资源，输出Derived destructor，然后输出Base destructor

    return 0;
}