为什么不执行此PHP？

我从这个网站精确复制代码：http://davidwalsh.name/web-service-php-mysql-xml-json如下，为什么不执行此PHP？

/* require the user as the parameter */ 
if(isset($_GET['user']) && intval($_GET['user'])) { 

/* soak in the passed variable or set our own */ 
$number_of_posts = isset($_GET['num']) ? intval($_GET['num']) : 10; //10 is the default 
$format = strtolower($_GET['format']) == 'json' ? 'json' : 'xml'; //xml is the default 
$user_id = intval($_GET['user']); //no default 

/* connect to the db */ 
$link = mysql_connect('localhost','username','password') or die('Cannot connect to the DB'); 
mysql_select_db('db_name',$link) or die('Cannot select the DB'); 

/* grab the posts from the db */ 
$query = "SELECT post_title, guid FROM wp_posts WHERE post_author = $user_id AND post_status = 'publish' ORDER BY ID DESC LIMIT $number_of_posts"; 
$result = mysql_query($query,$link) or die('Errant query: '.$query); 

/* create one master array of the records */ 
$posts = array(); 
if(mysql_num_rows($result)) { 
    while($post = mysql_fetch_assoc($result)) { 
     $posts[] = array('post'=>$post); 
    } 
} 

/* output in necessary format */ 
if($format == 'json') { 
    header('Content-type: application/json'); 
    echo json_encode(array('posts'=>$posts)); 
} 
else { 
    header('Content-type: text/xml'); 
    echo '<posts>'; 
    foreach($posts as $index => $post) { 
     if(is_array($post)) { 
      foreach($post as $key => $value) { 
       echo '<',$key,'>'; 
       if(is_array($value)) { 
        foreach($value as $tag => $val) { 
         echo '<',$tag,'>',htmlentities($val),'</',$tag,'>'; 
        } 
       } 
       echo '</',$key,'>'; 
      } 
     } 
    } 
    echo '</posts>'; 
} 

/* disconnect from the db */ 
@mysql_close($link); 
}

而且PHP不执行，它只是显示为纯文本。什么是dealio？主机支持PHP，我用它来运行一个WordPress博客和其他东西。

来源

2010-05-07 cam

在这个问题中：'我从互联网复制了一个代码并且它不工作' – 2010-05-07 22:44:41