使用提取php功能的问题？

 <?php  
 function check($user_id, $topic_id){

        $query = mysql_query("SELECT user_id, topic_id FROM sa where topic_id='$topic_id' and user_id='$user_id'");
        if (mysql_num_rows($query)==1){



           return 'you have already voted';
        }
        else {

            $against = ' <li>
    <button type="submit" value="Actions" class="against" title="against">
      <i></i><span>Against</span></button>
          </li>';

            $support ='<li>
            <button type="submit" value="Actions" class="support" title="support">
                <i></i>
                <span>Support</span>
            </button>
        </li>';
            return compact('support', 'against');
        }

extract(check($_SESSION['user_id'], $topicId));

  echo $against;
  echo $support;
?>

i keep getting this error:

Warning: extract() [function.extract]: First argument should be an array 

Maybe something like this is better:

function check($user_id, $topic_id){
    $query = mysql_query("SELECT user_id, topic_id FROM sa where topic_id='$topic_id' and user_id='$user_id'");
    if (mysql_num_rows($query)==1){
       return array('error'=>'you have already voted');
    }
    else {
        $against = ' <li>
<button type="submit" value="Actions" class="against" title="against">
  <i></i><span>Against</span></button>
      </li>';

        $support ='<li>
        <button type="submit" value="Actions" class="support" title="support">
            <i></i>
            <span>Support</span>
        </button>
    </li>';
        return compact('support', 'against');
    }
}

$result = check($_SESSION['user_id'], $topicId);

if(isset($result['error'])) {
    echo $result['error'];
}
else {
    echo $result['against'];
    echo $result['support'];
}

You could also consider to use exceptions.

First, function definition is not closed in your code (no closing "}")

Second, your function returns string if user has already voted - in this case PHP would obviously say "First argument should be an array" on extract() function call.

Generally, I'd recommend not to use compact-extract construction, but use structures or associative arrays as return value instead. In this case behavior would be much clearer.

The extract function expects an array. You're passing it the results of your check function, which is sometimes an array

return compact('support', 'against');

but sometimes a string.

return 'you have already voted';

So, I imagine you're seeing the error when the first return statements is executed.

So as it suggests: Warning: extract() [function.extract]: First argument should be an array

Try following:

$arr = check($_SESSION['user_id'], $topicId);
if(is_array($arr)) {
  extract($arr);
  echo $against;
  echo $support;
} else {
  echo $arr;
}