[boost] IOStreams basic_newline_filter convenience request

From: Jonathan Graehl (jonathan_at_[hidden])
Date: 2004-09-07 14:08:59

For basic_newline_filter (great idea; I hadn't even realized Macintosh 
had yet ANOTHER newline convention), it would be nice to be able to get 
the current line number and possibly even the character number on that 
line, for reporting errors in input.  I realize this should be possible 
as a separate filter counting '\n' and non-'\n' characters, which 
handles the output of basic_newline_filter, but I don't think the cost 
of maintaining one or two counters would be too much a burden for those 
who don't need it (or if it is, provide versions with and without).

Even nicer would be a call that extracts up to the previous N already 
consumed characters, for even more helpful context (I have already made 
a practice of showing the next N characters to be read in case of a 
fatal error, when the input is a file and not interactive).  Obviously 
this could be a filter in its own right, and really has nothing to do 
with basic_newline_filter.