# Wcswidth, ruby 1.9, and string encodings **URL:** \ **Category:** Ruby\ **Created:** [May 10, 2010, 3:30am UTC](https://www.ruby-forum.com/t/wcswidth-ruby-1-9-and-string-encodings/188309 "2010-05-10T03:30:00Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![trucker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ecae2f/32.png) [@trucker](https://www.ruby-forum.com/u/trucker)\ **Post date:** [May 10, 2010, 3:30am UTC](https://www.ruby-forum.com/t/wcswidth-ruby-1-9-and-string-encodings/188309/1 "2010-05-10T03:30:00Z")
Hello all, I need some advice about how to use wcswidth on Ruby 1.9 strings. Wcswidth returns the column width of a string, i.e. how much of the horizontal space on the screen a string takes up when printed to a terminal. Being able to calculate column width is crucial for any console-based program that deals with non-ASCII characters. For example, Chinese characters typically take up two columns. So, I’d like to write a gem that provides wcswidth to Ruby. I have a simple version that works: [ruby-wcswidth.c · GitHub](https://gist.github.com/729d17559ac523fabf39) Unfortunately, this code requires that the string’s encoding match your LC\_CTYPE, because mbstowcs relies on LC\_CTYPE to produce wchar\_t’s. If those don’t match, you’ll either get nothing, or, possibly, a wrong answer. So, is there a mapping between Ruby string encodings and LC\_CTYPE values? If so, I could at least check that the conversion is done correctly (or possibly even skip the mbstowcs step, if I know what wchar\_t is and what encoding corresponds to it–of course what wchar\_t means is system-dependent.) Or is there a better way to do this than using mbstowcs? Or heck, is there already a way of getting string column width in Ruby? It seems like there should be, but I don’t see one. Thanks! ---
**Author:** ![trucker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ecae2f/32.png) [@trucker](https://www.ruby-forum.com/u/trucker)\ **Post date:** [May 10, 2010, 5:42am UTC](https://www.ruby-forum.com/t/wcswidth-ruby-1-9-and-string-encodings/188309/2 "2010-05-10T05:42:53Z")
2010/5/10 William M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > I need some advice about how to use wcswidth on Ruby 1.9 strings. > Wcswidth returns the column width of a string, i.e. how much of the > horizontal space on the screen a string takes up when printed to a > terminal. Being able to calculate column width is crucial for any > console-based program that deals with non-ASCII characters. For example, > Chinese characters typically take up two columns. I wrote such code in my terminfo binding. > **[GitHub - akr/ruby-terminfo: terminfo binding for Ruby](https://github.com/akr/ruby-terminfo)** > > terminfo binding for Ruby. Contribute to akr/ruby-terminfo development by creating an account on GitHub. > Unfortunately, this code requires that the string’s encoding match your > LC\_CTYPE, because mbstowcs relies on LC\_CTYPE to produce wchar\_t’s. If > those don’t match, you’ll either get nothing, or, possibly, a wrong > answer. I used rb\_locale\_encoding() to convert to LC\_CTYPE as follows: str = rb\_str\_encode(str, rb\_enc\_from\_encoding(rb\_locale\_encoding()), 0, Qnil); ---
**Author:** ![trucker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ecae2f/32.png) [@trucker](https://www.ruby-forum.com/u/trucker)\ **Post date:** [May 10, 2010, 3:48pm UTC](https://www.ruby-forum.com/t/wcswidth-ruby-1-9-and-string-encodings/188309/3 "2010-05-10T15:48:10Z")
Reformatted excerpts from Tanaka A.'s message of 2010-05-09: > I wrote such code in my terminfo binding. > [GitHub - akr/ruby-terminfo: terminfo binding for Ruby](http://github.com/akr/ruby-terminfo) Very nice. It works when I use your git version. But the latest gem (v0.1.1) doesn’t seem to have wcswidth. > I used rb\_locale\_encoding() to convert to LC\_CTYPE as follows: > > str = rb\_str\_encode(str, rb\_enc\_from\_encoding(rb\_locale\_encoding()), 0, Qnil); Perfect, that’s what I was missing. I need one other bit of functionality too: the ability to get a substring of a specific display width. I assume that is beyond the scope of your terminfo package, so I am probably going to wrap the two methods up into a gem. But if you’re planning on adding such a thing to ruby-terminfo, let me know, and I will just use that instead. Thanks for your help! ---
**Author:** ![trucker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/ecae2f/32.png) [@trucker](https://www.ruby-forum.com/u/trucker)\ **Post date:** [May 19, 2010, 3:07pm UTC](https://www.ruby-forum.com/t/wcswidth-ruby-1-9-and-string-encodings/188309/4 "2010-05-19T15:07:58Z")
Reformatted excerpts from William M.'s message of 2010-05-10: > I need one other bit of functionality too: the ability to get a > substring of a specific display width. I assume that is beyond the > scope of your terminfo package, so I am probably going to wrap the two > methods up into a gem. I’ve finally pulled these together into a gem: [http://rubygems.org/gems/console](http://rubygems.org/gems/console) If anyone else is interested in writing i18n-capable console applications, this should be pretty useful for you. Unfortunately I haven’t quite gotten it to work with Ruby 1.8. Any help on that front would be appreciated. Blog post with a little more background: [http://all-thing.net/string-width](http://all-thing.net/string-width)