php preg_replace problem

$strSubject= preg_replace('/\b'.$strWord.'\b/i', '<b>'.$strWord.'</b>', $strSubject);    

above code works in php 5.2.6 but not wor开发者_如何转开发king in php 5.2.9 and get " warning,unknow modifer....." error. please help

You probably have a meta character unescaped in $strWord. Try this...

$strSubject= preg_replace('/\b'.preg_quote($strWord, '/').'\b/i', '<b>'.$strWord.'</b>', $strSubject);    

Also, you could just use this :)

$strSubject = preg_replace('/\b('.preg_quote($strWord, '/').')\b/i', '<b>$1</b>', $strSubject);