关于c:CUDA5.5nvlinkundefinedreference(inheritance)

1>nvlink : error : Undefined reference to '_ZN6ShaderD1Ev' in 'Debug/IShader.cu.obj'
1>nvlink : error : Undefined reference to '_ZN6ShaderD0Ev' in 'Debug/IShader.cu.obj'
1>nvlink : error : Undefined reference to '_ZN6ShaderD2Ev' in 'Debug/Lambert.cu.obj'

#include"Vector3D.cuh"
#include"Color.cuh"
#include"IGeometry.cuh"

__device__ extern Vector cameraPos;

__device__ extern Vector lightPos;

__device__ extern Color lightColor;

__device__ extern float lightPower;

__device__ extern Color ambientLight;

class Shader
{
protected:

     Color _color;

public:

    __device__ Shader(const Color& color);

    __device__ virtual ~Shader();

    __device__ virtual Color shade(Ray ray, const IntersectionData& data) = 0;
};

#endif

//IShader.cu
#include"IShader.cuh"

__device__ Shader::Shader(const Color& color)
{

   this->_color = color;
}

// Lambert.cuh
#ifndef LAMBERT_H
#define LAMBERT_H

#include"IShader.cuh"

class Lambert : public Shader
{
public:

    __device__ Lambert(const Color& diffuseColor);

    __device__ Color shade(Ray ray, const IntersectionData& data);
};

#endif

//Lambert.cu
#include"Lambert.cuh"

Vector cameraPos;

Vector lightPos;

Color lightColor;
float lightPower;

Color ambientLight;

__device__ Lambert::Lambert(const Color& diffuseColor)

    : Shader(diffuseColor)
{
}

__device__ Color Lambert::shade(Ray ray, const IntersectionData& data)
{

    Color result = _color;

    result = result * lightColor * lightPower / (data.p - lightPos).lengthSqr();

    Vector lightDir = lightPos - data.p;

    lightDir.normalize();

    double cosTheta = dot(lightDir, data.normal);

    result = result * cosTheta;

    return result;
}