为什么返回会添加换行符？

Question

I'm calling saveVideo.php via ajax and $result always has two linebreaks at the top, I don't see where they could be coming from. It should be simply the $id variable in addVideo. I need the id to ajax in the new video once it's uploaded.

Even with trim(), the output from the saveVideo ajax call in Developer tools has 2 linebreaks in front of it.

Here's all the relevant code:

saveVideo.php:

<?php
require_once '../model.php';

$m = new Model;
$video = new Video;

$user = requireLogin();


$video->file = $_POST['url'];
$video->lib = 0; //sets library to be personal.
$video->title = mysql_escape_string($_POST['video-title']);
$video->desc = mysql_escape_string($_POST['video-description']);
$video->userId = $user->id;

$result = $m->addVideo($video);

echo trim($result);
?>

the addVideo function:

function addVideo($video, $lib = 1) {
        // Adds video to database and associates it with a user id

        $qstring = "mysqlquery";

        $result = mysql_query($qstring);

        $id = mysql_insert_id();

        if (!$result) {
            die("Error adding video to database.");
        }
        return $id;
    }

Answer 1

Look for unnecessary blank lines before your opening <?php or after your closing ?> tags. If there are blank lines outside of a <?php ?> block they will be treated as part of the page content and be sent as part of the PHP response.

This applies to ../model.php as well. Blank lines in there will do the same thing.

---

Also, when you're debugging something like this you'll save a lot of hair pulling if you use var_dump rather than echo.

var_dump($result);

This would produce output like

string(2) "14"

which would tell you that $result is not the source of the mysterious line breaks.