为什么我的代码不起作用？这些例子之间只有一个变化。我想可能是$anchor类型的问题？
此代码无效：

<?php  
header('Content-Type: text/html; charset=utf-8');
$db = mysql_connect('localhost', 'db_name', 'db_pass'); 
mysql_select_db('db_name'); 
mysql_set_charset('utf8'); 
$res = mysql_query("SELECT * FROM product_description");
while($row = mysql_fetch_array($res)){ 

$anchor = strval($row['description']); //Only this string changed!

    $anchor = preg_replace(
        '@\\<a\\b[^\\>]*\\>(.*?)\\<\\/a\\b[^\\>]*\\>@',
        '\\1',
        $anchor
    );

echo $anchor;

}

mysql_close($db);
?>

但这段代码有效，我只更改了一个字符串：

<?php  
header('Content-Type: text/html; charset=utf-8');
$db = mysql_connect('localhost', 'db_name', 'db_pass'); 
mysql_select_db('db_name'); 
mysql_set_charset('utf8'); 
$res = mysql_query("SELECT * FROM product_description");
while($row = mysql_fetch_array($res)){ 

$anchor = 'Lorem ipsum <a href="http://www.google.es">Google</a> Lorem ipsum <a href="http://www.bing.com">Bing</a>'; //Only this string changed!

    $anchor = preg_replace(
        '@\\<a\\b[^\\>]*\\>(.*?)\\<\\/a\\b[^\\>]*\\>@',
        '\\1',
        $anchor
    );

echo $anchor;

}
mysql_close($db);
?>