C++ 虚析构

作用：

发生多态时，若想子类执行其析构行为，需要将父类的析构函数加上virtual关键字变成虚析构函数，这样才能保证在子类对象释放时执行到子类的析构行为

简单概括为：为了解决父类指针释放子类对象问题

父类析构未加virtual关键字：

#include <iostream>
#include <string>

class Animal
{
public:
	Animal()
	{
		std::cout << "Animal构造函数被调用" << std::endl;
	}

	//普通析构函数
	~Animal()
	{
		std::cout << "Animal析构函数被调用" << std::endl;
	}

	virtual void Speak() = 0;
};

class Cat :public Animal
{
public:
	Cat(std::string& name)
	{
		m_name = new std::string(name);
		std::cout << "Cat构造函数被调用" << std::endl;
	}

	~Cat()
	{
		if (m_name != nullptr)
		{
			delete m_name;
			m_name = nullptr;
		}

		std::cout << "Cat析构函数被调用" << std::endl;
	}

	virtual void Speak()
	{
		std::cout << *m_name << "小猫在说话" << std::endl;
	}

	std::string* m_name;
};

int main()
{
	std::string name = "Tom";
	Animal* animal = new Cat(name);
	animal->Speak();
	if (animal != nullptr)
	{
		delete animal;
		animal = nullptr;
	}

	system("pause");
	return 0;
}

 

父类析构为虚析构： 

#include <iostream>
#include <string>

class Animal
{
public:
	Animal()
	{
		std::cout << "Animal构造函数被调用" << std::endl;
	}

	//虚析构函数
	virtual ~Animal()
	{
		std::cout << "Animal析构函数被调用" << std::endl;
	}

	virtual void Speak() = 0;
};

class Cat :public Animal
{
public:
	Cat(std::string& name)
	{
		m_name = new std::string(name);
		std::cout << "Cat构造函数被调用" << std::endl;
	}

	~Cat()
	{
		if (m_name != nullptr)
		{
			delete m_name;
			m_name = nullptr;
		}

		std::cout << "Cat析构函数被调用" << std::endl;
	}

	virtual void Speak()
	{
		std::cout << *m_name << "小猫在说话" << std::endl;
	}

	std::string* m_name;
};

int main()
{
	std::string name = "Tom";
	Animal* animal = new Cat(name);
	animal->Speak();
	if (animal != nullptr)
	{
		delete animal;
		animal = nullptr;
	}

	system("pause");
	return 0;
}

总结： 

• 发生多态时，只有父类存在虚析构函数，子类的析构函数才能被执行，否则容易发生内存泄漏。