[boost] [range] sub_range of istream_range

I’m trying to iterate through a file using sub_ranges of an istream_range of an ifstream. However, it seems if I construct sub ranges of various subsets of the full istream_range, try to adjust the limits with advance_begin and advance_end, and then access them I get null dereferences. Any thoughts? I can produce an example if needed. Cheers! Andrew Hundt