Hi,
please check out this guide on posting code to make your post more readable.
A segmentation fault with a stacktrace that involves code under EnteringUserCode most probably means that you have a bug in your code, most likely you are accessing a null pointer or non-existent array elements.
My advice would be to check that ntuple is not a nullptr, that row is not a nullptr, and that row has really 3 elements.
Cheers,
Enrico