Re: [boost] [libboost_regex-1_32.dylib] Validating Email address usingRegx failing in boost

Subject: Re: [boost] [libboost_regex-1_32.dylib] Validating Email address usingRegx failing in boost
From: John Maddock (john_at_[hidden])
Date: 2009-10-22 12:05:30

> I am using boost regex libraries (libboost_regex-1_32.dylib) for
> validation of strings. The regular expression string i use is as
> below.
>
> string expr = 
> "^((?>[a-zA-Z\\d!#$%&'*+\\-/=?^_`{|}~]+\\x20*|\"((?=[\\x01-\\x7f])[^\"\\\\]|\\\\[\\x01-\\x7f])*\"\\x20*)*(?<angle><))?((?!\\.)(?>\\.?[a-zA-Z\\d!#$%&'*+\\-/=?^_`{|}~]+)+|\"((?=[\\x01-\\x7f])[^\"\\\\]|\\\\[\\x01-\\x7f])*\")@(((?!-)[a-zA-Z\\d\\-]+(?<!-)\\.)+[a-zA-Z]{2,}|\\[(((?(?<!\\[)\\.)(25[0-5]|2[0-4]\\d|[01]?\\d?\\d)){4}|[a-zA-Z\\d\\-]*[a-zA-Z\\d]:((?=[\\x01-\\x7f])[^\\\\\\[\\]]|\\\\[\\x01-\\x7f])+)\\])(?(angle)>)$";
>
> When i make a call
>
> boost::regex regExpr(expr);
>
> it is throwing  what():  Invalid preceding regular expression.

Sigh... I *really* need to improve those error messages :-(

I tried the expression in Perl and got an error as well:

$in = 'name.surname_at_[hidden]';
$in =~ 
/^((?>[a-zA-Z\d!#$%&'*+\-\/=?^_`{|}~]+\x20*|"((?=[\x01-\x7f])[^"\\]|\\[\x01-\x7f])*"\x20*)*(?<angle><))?((?!\.)(?>\.?[a-zA-Z\d!#$%&'*+\-\/=?^_`{|}~]+)+|"((?=[\x01-\x7f])[^"\\]|\\[\x01-\x7f])*")@(((?!-)[a-zA-Z\d\-]+(?<!-)\.)+[a-zA-Z]{2,}|\[(((?(?<!\[)\.)(25[0-5]|2[0-4]\d|[01]?\d?\d)){4}|[a-zA-Z\d\-]*[a-zA-Z\d]:((?=[\x01-\x7f])[^\\\[\]]|\\[\x01-\x7f])+)\])(?(angle)>)$/;
print "\n";
   print "\$& = $&\n";
   print "\$1 = $1\n";
   print "\$2 = $2\n";
   print "\$3 = $3\n";
   print "\$4 = $4\n";
   print "\$5 = $5\n";
   print "\$6 = $6\n";
   print "\$7 = $7\n";
   print "\$8 = $8\n";

Prints:

Unknown switch condition (?(an in regex; marked by <-- HERE in 
m/^((?>[a-zA-Z\d!#0&'*+\-/=?^_`{|}~]+\x20*|"((?=[\x01-\x7f])[^"\\]|\\[\x01-\x7f])*"\x20*)*(?<angle><))?((?!\.)(?>\.?[a-zA-Z\d!#0&'*+\-/=?^_`{|}~]+)+|"((?=[\x01-\x7f])[^"\\]|\\[\x01-\x7f])*")@(((?!-)[a-zA-Z\d\-]+(?<!-)\.)+[a-zA-Z]{2,}|\[(((?(?<!\[)\.)(25[0-5]|2[0-4]\d|[01]?\d?\d)){4}|[a-zA-Z\d\-]*[a-zA-Z\d]:((?=[\x01-\x7f])[^\\\[\]]|\\[\x01-\x7f])+)\])(?( 
<-- HERE angle)>)$/ at test.pl line 3.

So Perl and Boost.Regex are both rejecting the "(?(angle)>)" part, and 
looking at http://perldoc.perl.org/perlre.html I believe it should be 
rejected.  It appears this is a .NET-specific construct :-(

Changing to "(?(<angle>)>)" seems to make everything work though, in code:

   boost::regex test ( 
"^((?>[a-zA-Z\\d!#$%&'*+\\-/=?^_`{|}~]+\\x20*|\"((?=[\\x01-\\x7f])[^\"\\\\]|\\\\[\\x01-\\x7f])*\"\\x20*)*(?<angle><))?((?!\\.)(?>\\.?[a-zA-Z\\d!#$%&'*+\\-/=?^_`{|}~]+)+|\"((?=[\\x01-\\x7f])[^\"\\\\]|\\\\[\\x01-\\x7f])*\")@(((?!-)[a-zA-Z\\d\\-]+(?<!-)\\.)+[a-zA-Z]{2,}|\\[(((?(?<!\\[)\\.)(25[0-5]|2[0-4]\\d|[01]?\\d?\\d)){4}|[a-zA-Z\\d\\-]*[a-zA-Z\\d]:((?=[\\x01-\\x7f])[^\\\\\\[\\]]|\\\\[\\x01-\\x7f])+)\\])(?(<angle>)>)$" 
 );

HTH, John.