无格式转换php

// 无格式转换
function ClearHtml($content,$allowtags='') {

mb_regex_encoding('UTF-8');
//replace MS special characters first
$search = array('/‘/u', '/’/u', '/“/u', '/”/u', '/—/u');
$replace = array('\'', '\'', '"', '"', '-');
$content = preg_replace($search, $replace, $content);
//make sure _all_ html entities are converted to the plain ascii equivalents - it appears
//in some MS headers, some html entities are encoded and some aren't
$content = html_entity_decode($content, ENT_QUOTES, 'UTF-8');
//try to strip out any C style comments first, since these, embedded in html comments, seem to
//prevent strip_tags from removing html comments (MS Word introduced combination)
if(mb_stripos($content, '/*') !== FALSE){
$content = mb_eregi_replace('#/\*.*?\*/#s', '', $content, 'm');
}
//introduce a space into any arithmetic expressions that could be caught by strip_tags so that they won't be
//'<1' becomes '< 1'(note: somewhat application specific)
$content = preg_replace(array('/<([0-9]+)/'), array('< $1'), $content);

$content = strip_tags($content, $allowtags);
//eliminate extraneous whitespace from start and end of line, or anywhere there are two or more spaces, convert it to one
$content = preg_replace(array('/^\s\s+/', '/\s\s+$/', '/\s\s+/u'), array('', '', ' '), $content);
//strip out inline css and simplify style tags
$search = array('#<(strong|b)[^>]*>(.*?)</(strong|b)>#isu', '#<(em|i)[^>]*>(.*?)</(em|i)>#isu', '#<u[^>]*>(.*?)</u>#isu');
$replace = array('<b>$2</b>', '<i>$2</i>', '<u>$1</u>');
$content = preg_replace($search, $replace, $content);

//on some of the ?newer MS Word exports, where you get conditionals of the form 'if gte mso 9', etc., it appears
//that whatever is in one of the html comments prevents strip_tags from eradicating the html comment that contains
//some MS Style Definitions - this last bit gets rid of any leftover comments */
$num_matches = preg_match_all("/\<!--/u", $content, $matches);
if($num_matches){
$content = preg_replace('/\<!--(.)*--\>/isu', '', $content);
}
return $content;
}
//
echo ClearHtml($content,'<p>');