Bei folgendem Code

#ifndef SHAPES_H_
#define SHAPES_H_

#include <string>
#include <cassert>

class AbstractShape
{
public:
	AbstractShape(void);
	virtual ~AbstractShape(void);

	virtual double area () const = 0;

	void setDescription(std::string const & str)
	{
		m_description = str;
	}
private:
	std::string m_description;
};

class RectShape : public AbstractShape
{
public:
	RectShape(void) : AbstractShape(), m_width(0), m_height(0)
	{
			setDescription("Rectangular Shape");
	}

	RectShape(const RectShape & s) 
	{
		this->m_width = s.m_width;
		this->m_height = s.m_height;
	}

	const RectShape& operator=(const RectShape& rhs)
	{
		if (this != &rhs) 
		{
			this->m_width = rhs.m_width;
			this->m_height = rhs.m_height;
		}
		return *this; // return self-reference so cascaded assignment works
	}

	virtual ~RectShape(void);

	void setSize(double width, double height)
	{
		setWidth(width);
		setHeight(height);
	}

	void setWidth(double width)
	{
		assert(width > 0);
		m_width = width;
	}
	void setHeight(double height)
	{
		assert(height > 0);
		m_height = height;
	}

	double area () const
	{
		return (m_width * m_height);
	}

private:
	double m_width;
	double m_height;

};

#endif

und

// main.cpp 
#include "Shapes.h"
int main(int argc, char** argv)
{
	RectShape rectShape;	
}

bekomme ich die Linkerfehler:

1>main.obj : error LNK2019: Verweis auf nicht aufgelöstes externes Symbol ""public: virtual __thiscall AbstractShape::~AbstractShape(void)" (??1AbstractShape@@UAE@XZ)" in Funktion "__unwindfunclet$??0RectShape@@QAE@XZ$0".
1>main.obj : error LNK2019: Verweis auf nicht aufgelöstes externes Symbol ""public: __thiscall AbstractShape::AbstractShape(void)" (??0AbstractShape@@QAE@XZ)" in Funktion ""public: __thiscall RectShape::RectShape(void)" (??0RectShape@@QAE@XZ)".
1>main.obj : error LNK2019: Verweis auf nicht aufgelöstes externes Symbol ""public: virtual __thiscall RectShape::~RectShape(void)" (??1RectShape@@UAE@XZ)" in Funktion ""public: virtual void * __thiscall RectShape::`scalar deleting destructor'(unsigned int)" (??_GRectShape@@UAEPAXI@Z)".

warum?