glutKeyboardFunc(keyboard);函数出错

我写的键盘回调函数
void keyboard(unsigned char key, int x, int y)
{
float step = 10.0;
float angle = 5.0;

switch(key)
{
case 27:
exit(0);
break;

case 'w':
// move forward: MoveForward(step);
glutPostRedisplay();
break;

case 's':
// move backward: MoveBackward(step);
glutPostRedisplay();
break;

case 'a':
// move left: MoveLeft(step);
glutPostRedisplay();
break;

case 'd':
// move right: MoveRight(step);
glutPostRedisplay();
break;

case 'r':
// move up: MoveUp(step);
glutPostRedisplay();
break;

case 'f':
// move down: MoveDown(step);
glutPostRedisplay();
break;

case 'q':
// roll left: RollLeft(angle);
glutPostRedisplay();
break;

case 'e':
// roll right: RollRight(angle);
glutPostRedisplay();
break;

case ' ':
/*
cam_type=1-cam_type;
if (cam_type==0) p_cam=&theFPCam;
else p_cam=&theFreeCam;
p_cam->SetPosition(CVector3D(500.0, 0.0, 100.0));
p_cam->SetAxes(CVector3D(0,1,0), CVector3D(0,0,1), CVector3D(1,0,0));
*/
glutPostRedisplay();
break;
}
}

调用时使用语句：glutKeyboardFunc(keyboard);

编译时产生错误：error C2664: 'glutKeyboardFunc' : cannot convert parameter 1 from 'void (unsigned char,int,int)' to 'void (__cdecl *)(unsigned char,int,int)'
None of the functions with this name in scope match the target type

OpenGL头文件已添加，void keyboard(unsigned char key, int x, int y)函数也已声明，请问怎么改？