如果你已经有一个boost依赖（这些天，很多人都这样做），你可以使用boost 多精度库。事实上，它已经有一个例子： factorial program ，它可以支持高达128位的输出，虽然扩展更多是非常微不足道的。

If you already have a boost dependency (which many people these days do), you can use the boost multi-precision library. In fact, it already has an example of a factorial program that can support output up to 128 bits, though extending it further is pretty trivial.