Hello,
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If you want to use c++ methods in UWP, the first suggestion is to wrap that C++ logic using a WinRT component.
But if you want to directly use your c++ library, you can PInvoke the dll. You need to follow these steps (You can also refer to this thread for more details):
First, add .dll into your UWP project making sure to set its type as 'content'.
Then in the proper .cs file, using DllImport to PInvoke the dll. And here is a similar thread, you can refer to it.
Thanks.