Bug #3482

StringScanner#pos returns wrong character position if used with multibyte chars

Added by Marvin Gülker over 5 years ago. Updated over 4 years ago.

ruby -v:ruby 1.9.2dev (2010-05-31 revision 28117) [x86_64-linux] Backport:


The StringScanner class from 1.9's stdlib works on bytes rather than on characters. That means, if you want to extract substrings from the original string by use of the return value of StringScanner#pos you get incorrect results:

irb(main):001:0> require "strscan"
=> true
irb(main):002:0> str = "abcädeföghi"
=> "abcädeföghi"
irb(main):003:0> ss = StringScanner.new(str)
=> #
irb(main):004:0> ss.scan_until(/ä/)
=> "abcä"
irb(main):005:0> ss.pos
=> 5
irb(main):006:0> ss.scan_until(/ö/)
=> "defö"
irb(main):007:0> ss.pos
=> 10

After the first scan_until I expected the position to be 4, after the second to be 8, which means we finally have an offset of 2 here.

My Ruby version is ruby 1.9.1p378 (2010-01-10 revision 26273) [x86_64-linux], but I also get the same beaviour with the 1.9.2-preview3 (ruby 1.9.2dev (2010-05-31 revision 28117) [x86_64-linux]).

Related issues

Related to Ruby trunk - Feature #1159: StringScanner に文字ベースでのインデックスを返すメソッドがほしい Rejected 02/14/2009


#1 Updated by Yusuke Endoh over 5 years ago

  • Status changed from Open to Rejected


It is a spec. See rdoc of StringScanner#pos.

FYI, IO#pos is also byte-oriented.
I guess this is because #pos is supposed to be byte-oriented.

Yusuke Endoh mame@tsg.ne.jp

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