how to pass bitmap data type to c++ dll ?

[DllImport("dllTestForm.dll", EntryPoint = "showFormC")]
static extern void testShowFormC(byte[] photo,int len);

private void button6_Click(object sender, EventArgs e)
{
		Bitmap bmp = (Bitmap)Image.FromFile(@"d:\1\1.jpg");

		Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height);
		System.Drawing.Imaging.BitmapData bmpData =
		bmp.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadWrite,bmp.PixelFormat);

		// Get the address of the first line.
		IntPtr ptr = bmpData.Scan0;

		// Declare an array to hold the bytes of the bitmap. 
		int bytes  = Math.Abs(bmpData.Stride) * bmp.Height;
		byte[] rgbValues = new byte[bytes];

		 // Copy the RGB values into the array.
		 System.Runtime.InteropServices.Marshal.Copy(ptr, rgbValues, 0, bytes);

		 // Unlock the bits.
		 bmp.UnlockBits(bmpData);

		 testShowFormC(rgbValues, bytes);
}

[DllImport("dllTestForm.dll", EntryPoint = "showFormC")]
static extern void testShowFormC(byte[] photo,int len);

void __stdcall showFormC(byte *photo,int len)
{
    ThelloWorld *a=new ThelloWorld(Application);//这是一个winForm测试界面,显示图片用
    a->ImageEnView2->IO->LoadFromBuffer(photo,0,len);  
    a->Show();

}