虚函数和虚析构函数在调用的处理上是不同的，虚析构函数是子调用父，层层调用，对于普通的虚函数，则是重载的方式，需要注意。下面的代码执行结果是：

derivedA say: hello virtual function!.
~finalA
~derivedA
~baseA

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
 
class baseA{
public:
	virtual ~baseA()
		{
			printf("~baseA\r\n");
		};
	virtual void sayHello(const char *str){
		printf("baseA say: %s.\r\n", str);
	};
};
 
class derivedA : public baseA {
public:
	virtual ~derivedA()
		{
			printf("~derivedA\r\n");
		};
	virtual void sayHello(const char *str){
		printf("derivedA say: %s.\r\n", str);
	};
};
 
class finalA : public derivedA {
public:
	~finalA()
		{
			printf("~finalA\r\n");
		};
	void sayHello(const char *str){
		printf("derivedA say: %s.\r\n", str);
	};
};
 
int main()
{
	finalA *a = new finalA();
	a->sayHello("hello virtual function!");
	delete a;
    return 0;
}