virtual destructors

[zwA4jE8b]

Can anyone tell me the proper way to implement a virtual destructor?
any maybe even why it is the way it is.
I read that the derived objects destructor will automatically call the base objects destructor when invoked. i.e. delete

class obj_holder
{
	protected:
		float x, y;
		float x_vel, y_vel;
		float tem_grav;
		float air_time;
		bool moving;
	public:
		virtual void handle_input();
		virtual void move();
		virtual void show();
		virtual ~obj_holder();
};

//tried with and without this
obj_holder::~obj_holder(){};

//The man
class Man: public obj_holder
{
    public:
		Man();
		void handle_input();
		void move();
		void show();
		~Man();
};

//The ball
class Ball: public obj_holder
{
    private:
		float t_vel;

    public:
		Ball();
		void handle_input();
		void direction(float, float);
		void move();
		void show();
		~Ball();
};

.....
.....
.....

Man::~Man(){}
Ball::~Ball(){}

Errors using empty implementation
[output]src\main.o:main.cpp:(.text+0x96): undefined reference to `vtable for obj_holder'
src\main.o:main.cpp:(.text+0xa2): undefined reference to `vtable for obj_holder'
src\main.o:main.cpp:(.text+0xae): undefined reference to `vtable for obj_holder'
src\main.o:main.cpp:(.text+0xbe): undefined reference to `vtable for obj_holder'
src\main.o:main.cpp:(.text+0x302): undefined reference to `vtable for obj_holder'
src\main.o:main.cpp:(.text+0x30e): more undefined references to `vtable for obj_holder' follow[/output]

errors not using empty implementation

src\main.o:main.cpp:(.text+0xb2): undefined reference to `obj_holder::~obj_holder()'
src\main.o:main.cpp:(.text+0xe6): undefined reference to `obj_holder::~obj_holder()'
src\main.o:main.cpp:(.text+0x9b): undefined reference to `obj_holder::~obj_holder()'
src\main.o:main.cpp:(.text+0xcf): undefined reference to `obj_holder::~obj_holder()'

src\main.o:main.cpp:(.text$_ZN3ManD1Ev[Man::~Man()]+0x6): undefined reference to `vtable for obj_holder'
src\main.o:main.cpp:(.text$_ZN4BallD1Ev[Ball::~Ball()]+0x6): undefined reference to `vtable for obj_holder'
src\main.o:main.cpp:(.text$_ZN4BallD0Ev[Ball::~Ball()]+0x6): undefined reference to `vtable for obj_holder'
src\main.o:main.cpp:(.text$_ZN3ManD0Ev[Man::~Man()]+0x6): undefined reference to `vtable for obj_holder'

[Peter87]

Implement a definition of the virtual functions in obj_holder or make them pure virtual.

[zwA4jE8b]

Thanks Peter87

This works!

class obj_holder
{
	protected:
		float x, y;
		float x_vel, y_vel;
		float tem_grav;
		float air_time;
		bool moving;
	public:
		virtual void handle_input(){};
		virtual void move(){};
		virtual void show(){};
		virtual ~obj_holder(){};
};

This does not work!

class obj_holder
{
	protected:
		float x, y;
		float x_vel, y_vel;
		float tem_grav;
		float air_time;
		bool moving;
	public:
		virtual void handle_input() = 0;
		virtual void move() = 0;
		virtual void show() = 0;
		virtual ~obj_holder() = 0;
};

src\main.o:main.cpp:(.text+0xb2): undefined reference to `obj_holder::~obj_holder()'
src\main.o:main.cpp:(.text+0xe6): undefined reference to `obj_holder::~obj_holder()'
src\main.o:main.cpp:(.text+0x9b): undefined reference to `obj_holder::~obj_holder()'
src\main.o:main.cpp:(.text+0xcf): undefined reference to `obj_holder::~obj_holder()'

do you happen to know why?

[Peter87]

If you make the destructor pure virtual you still need to define the destructor.

[zwA4jE8b]

Cool, thank you.

This works too!

class obj_holder
{
	protected:
		float x, y;
		float x_vel, y_vel;
		float tem_grav;
		float air_time;
		bool moving;
	public:
		virtual void handle_input()=0;
		virtual void move()=0;
		virtual void show()=0;
		virtual ~obj_holder() = 0;
};

obj_holder::~obj_holder(){std::cout << "~obj_holder ";}

[zwA4jE8b]

one last question...

If I leave the implementation blank it still destructs properly, correct?
The memory is deallocated when I call delete?

or do I have to write delete this; in the destructor?

[bluecoder]

Hi ,
There is no need to make the virtual destructor as pure .

class obj_holder
{
	protected:
		float x, y;
		float x_vel, y_vel;
		float tem_grav;
		float air_time;
		bool moving;
	public:
		virtual void handle_input() = 0;
		virtual void move() = 0;
		virtual void show() = 0;
		virtual ~obj_holder() {}     //changed over here . 
};

cheers

[zwA4jE8b]

cool, both ways work. Is there any difference? besides one extra line of code?

[bluecoder]

there is no need to write this

Cheers :)

[zwA4jE8b]

sweet, thanks guys!