[Octave-bug-tracker] [bug #52479] textscan ignores leading spaces when creating cell from string/file

[Dan Sebald]

Follow-up Comment #2, bug #52479 (project octave):

It looks like the scanning routines all do skipping of white space in some
form:


  textscan::scan_one (delimited_stream& is, const textscan_format_elt& fmt,
                      octave_value& ov, Array<octave_idx_type> row)
  {
    skip_whitespace (is);


However, at the instantiation, the default white space includes the \t
character:


  textscan::textscan (const std::string& who_arg)
    : who (who_arg), buf (), whitespace_table (), delim_table (),
      delims (), comment_style (), comment_len (0), comment_char (-2),
      buffer_size (0), date_locale (), inf_nan (init_inf_nan ()),
      empty_value (numeric_limits<double>::NaN ()), exp_chars ("edED"),
      header_lines (0), treat_as_empty (), treat_as_empty_len (0),
      whitespace (" \b\t"), eol1 ('\r'), eol2 ('\n'),
      return_on_error (1), collect_output (false),
      multiple_delims_as_one (false), default_exp (true), lines (0)
  { }


To confirm this hypothesis, note that using a comma as a delimiter works:


octave:1> a = ",,a,b,c\n"
a = ,,a,b,c

octave:3> textscan(a, '%s', 'delimiter', sprintf(','))
ans =
{
  [1,1] =
  {
    [1,1] = 
    [2,1] = 
    [3,1] = a
    [4,1] = b
    [5,1] = c
  }

}


What needs to be done is remove any delimiters from the whitespace string.
That is, if the user selects


'delimiter', sprintf('\t'))


as you've done, then that character should be subtracted from the string.

I'm attaching a patch that does just that.  It seems to be in a reasonable
location for modifying the whitespace list, although I do see a lot of
"isspace()" used throughout the textscan code; so whether the patch catches
everything, I'm not sure.  Perhaps JWE and Rik can review for a more efficient
use of strings or general fix.

(file #42460)
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Additional Item Attachment:

File name: octave-textscan_whitespace_delimiter-djs2017nov22.patch Size:1 KB


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