php bbcode过滤

<?php
function bb_parse($string)
{
    $tags = 'b|i|size|color|center|quote|url|img';
    while (preg_match_all('`\[(' . $tags . ')=?(.*?)\](.+?)\[/\1\]`', $string, $matches))
    {
        foreach ($matches[0] as $key => $match) {
            list($tag, $param, $innertext) = array(
                $matches[1][$key],
                $matches[2][$key],
                $matches[3][$key]
            );
            switch ($tag) {
                case 'b':
                    $replacement = "<strong>$innertext</strong>";
                    break;
                case 'i':
                    $replacement = "<em>$innertext</em>";
                    break;
                case 'size':
                    $replacement = "<span style=\"font-size: $param;\">$innertext</span>";
                    break;
                case 'color':
                    $replacement = "<span style=\"color: $param;\">$innertext</span>";
                    break;
                case 'center':
                    $replacement = "<div class=\"centered\">$innertext</div>";
                    break;
                case 'quote':
                    $replacement = "<blockquote>$innertext</blockquote>" . $param ? "<cite>$param</cite>" : '';
                    break;
                case 'url':
                    $replacement = '<a href="' . ($param ? $param : $innertext) . "\">$innertext</a>";
                    break;
                case 'img':
                    @list($width, $height) = preg_split('`[Xx]`', $param);
                    $replacement = "<img src=\"$innertext\" " . (is_numeric($width) ? "width=\"$width\" " : '') . (is_numeric($height) ? "height=\"$height\" " : '') . '/>';
                    break;
            }
            $string = str_replace($match, $replacement, $string);
        }

    }
    return $string;
}


$text = <<<EOF
[b]Bold Text[/b]
[i]Italic Text[/i]
[url]http://www.php.net/[/url]
[url=http://pecl.php.net/][b]Content Text[/b][/url]
[img]http://static.php.net/www.php.net/images/php.gif[/img]
[url=http://www.php.net/][img]http://static.php.net/www.php.net/images/php.gif[/img][/url]
EOF;

echo bb_parse($text);

echo strip_tags( bb_parse($text) );
?> 

$cont_str = trim( preg_replace("/\[.*\]/", '', $cont_str) );