为什么在尝试编译此代码时会收到错误“error：unknown type name'virtual'”？

Code:

struct IRenderingEngine {
    virtual void Initialize(int width, int height) = 0;
    virtual void Render() const = 0;
    virtual void UpdateAnimation(float timeStep) = 0;
    virtual void OnRotate(DeviceOrientation newOrientation) = 0;
    virtual ~IRenderingEngine() {}
};
struct IRenderingEngine {
    virtual v