Virtual析构函数

Virtual析构函数

virtual析构函数确保在通过基类指针删除派生类对象时，能够正确调用派生类的析构函数，从而防止资源泄露

无virtual析构函数的问题

当基类的析构函数不是virtual时，通过基类指针delete对象，只会调用基类的析构函数，派生类的析构函数会被完全忽略

#include <iostream>

class Base {
public:
    Base() { std::cout << "Base constructor\n"; }
    // 非虚析构函数
    ~Base() { std::cout << "Base destructor\n"; }
};

class Derived : public Base {
private:
    int* data_;
public:
    Derived() { 
        data_ = new int[100]; // 派生类申请了资源
        std::cout << "Derived constructor, allocated data\n";
    }
    ~Derived() {
        delete[] data_; // 派生类释放资源
        std::cout << "Derived destructor, freed data\n";
    }
};

int main() {
    Base* ptr = new Derived(); // 用基类指针指向派生类对象
    delete ptr;                // 通过基类指针删除
    return 0;
}

virtual析构函数的解决方案

在基类的析构函数前加上virtual关键字

#include <iostream>

class Base {
public:
    Base() { std::cout << "Base constructor\n"; }
    // 虚析构函数
    virtual ~Base() { std::cout << "Base destructor\n"; }
};

// Derived类的代码保持不变
class Derived : public Base {
private:
    int* data_;
public:
    Derived() { 
        data_ = new int[100];
        std::cout << "Derived constructor, allocated data\n";
    }
    ~Derived() {
        delete[] data_;
        std::cout << "Derived destructor, freed data\n";
    }
};

int main() {
    Base* ptr = new Derived();
    delete ptr;
    return 0;
}

先调用派生类析构函数释放派生类资源，再调用基类析构函数。内存被完美释放