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

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