Hi All, 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)>)$"; When i make a call boost::regex regExpr(expr); it is throwing what(): Invalid preceding regular expression. I got the regular expression from http://regexlib.com/REDetails.aspx?regexp_id=711 and converted into std::string. If i print the string onto a terminal, the string exactly matches with the regular expression ^((?>[a-zA-Z\d!#$%&'*+\-/=?^_`{|}~]+\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)>)$ I am not able to find why boost is telling the string as invalid regular expression. I work in Mac OS X Leopard, and use boost_1_32. Any ideas? Thanks Arun Reply Forward New window Print all « Back to Sent Mail Archive Report spam Delete Move to Inbox Labels More actions 1 of 598 Older › Use free POP access to download your messages to Outlook or devices that support POP. Learn more You are currently using 1306 MB (17%) of your 7382 MB. Last account activity: 9 minutes ago at this IP (125.16.133.35). Details Gmail view: standard | turn off chat | older version | basic HTML Learn more ©2009 Google - Terms - Privacy Policy - Google Home