id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
13156,Not word boundary -  \b   vs. NOT \B are not the same,anonymous,John Maddock,"I am reposting this from another source. 

In theory, \B should match everywhere \b doesn't.  

In boost regex, this is not the case at the beginning nor end of string.  

Below is a list of test results from a few Perl-like engines.  
Apparently, this was fixed in Perl v5.22 (below shows v5.20).  
The only engines that seem to handle this correctly is PHP and
ECMAScript.  

------------------------------------------------

{{{

Target      = '   ssssssssssssss '
Replacement = '<>'

==================================================
PHP 7.03

\b      = '   <>ssssssssssssss<> '
\B      = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?!\b)  = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?<!\b) = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?!\B)  = '   <>ssssssssssssss<> '
(?<!\B) = '   <>ssssssssssssss<> '


=======================================
Perl 5.20

\b      = '   <>ssssssssssssss<> '
\B      = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s '
(?!\b)  = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?<!\b) = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?!\B)  = '   <>ssssssssssssss<> '
(?<!\B) = '   <>ssssssssssssss<> '

========================================
Boost 1.64

\b      = '   <>ssssssssssssss<> '
\B      = ' <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s '
(?!\b)  = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?<!\b) = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?!\B)  = '<>   <>ssssssssssssss<> <>'
(?<!\B) = '<>   <>ssssssssssssss<> <>'

=====================================
JavaScript

\b      = '   <>ssssssssssssss<> '
\B      = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?!\b)  = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?!\B)  = '   <>ssssssssssssss<> '

}}}
",Bugs,new,To Be Determined,regex,Boost 1.64.0,Showstopper,,Not Word Boundary \B,