Windows函数取消窗口自带阴影

HWND hwnd = reinterpret_cast<HWND>(m_pSettingMenu->winId());
if (hwnd)
{
DWORD class_style = ::GetClassLong(hwnd, GCL_STYLE);
class_style &= ~CS_DROPSHADOW;
::SetClassLong(hwnd, GCL_STYLE, class_style); // windows系统函数 
}