基类指针指向派生类对象，基类指针的首地址永远指向子类从基类继承的基类首地址

文章目录

• • • 基类指针指向派生类对象，基类指针的首地址永远指向子类从基类继承的基类起始地址。
    • 代码
    • 代码2

基类指针指向派生类对象，基类指针的首地址永远指向子类从基类继承的基类起始地址。

代码

#include <iostream>
using namespace std;

class base
{
public:
	void show() { cout << "base:: show"; }
};

class derive:public base
{
public:
	virtual void show() { cout << "derive:: show"; }
};

int main()
{
	base* p = new derive;
	p->show();
	delete p;
}

以上代码在调用delete 的时候出错，因为在调用deletes时传入的地址和我么预想的不一样，才会导致软件崩溃

代码2

#include <iostream>
using namespace std;

class base
{
public:
	void show() { cout << "base:: show"<<endl; }
	void operator delete(void *p)
	{
		cout << "operator delete p" <<p<< endl;
		free(p);
	}
};

class derive:public base
{
public:
	virtual void show() { cout << "derive:: show"; }
	void* operator new (size_t size)
	{
		void* p = malloc(size);
		cout << "operator new " << p << endl;
		return p;
	}
};

int main()
{
	base* p = new derive;
	p->show();
	delete p;
}

综上，子类带虚函数，而基类不带虚函数是一件非常危险的操作，编译器对指针的指向超出我们的预期，往往导致很难排查的问题