[RESOLVED] mysqli_query error (I'm stumped)

[agk]

Hello, I've been looking around for a bit, but I can't seem to figure out why my query is apparently not working.
Here are the errors I'm getting:

"Warning: mysqli_query() expects parameter 1 to be mysqli, null given in C:...\film.php on line 11
Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, null given in C:...\film.php on line 12
Query that didn't work: SELECT COUNT(*) FROM movielist WHERE movie_id = 1
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at C:...\film.php:11) in C:...\includes\header.php on line 14"

Here's my code...

function checkFilmExists($id)
{
    $q = 'SELECT COUNT(*) FROM movielist WHERE movie_id = '.$id;
    $r = mysqli_query($dbc, $q); // <-- line 11
    $row = mysqli_fetch_array($r);
    if($row['COUNT(*)'] == 1)
    {
        return true;
    }
    else
    {
        echo 'Query that didn\'t work: ' . $q;
        return false;
    }
}

if( (isset($_GET['id'])) && (is_numeric($_GET['id'])) && (checkFilmExists($_GET['id'])) )
{
    $id = $_GET['id'];
    $filmInfo = getFilmInfo($id);
    $error = false;
}
else
{
    $error = true;
}

When I put the query that it spits out ("SELECT COUNT(*) FROM movielist WHERE movie_id = 1") into my database manually, it works properly and returns 1 or 0 depending if the record exists or not.
I'm using $dbc as my database connection on some other pages right now and it is working properly, so I'm not sure where the issue is.
If anyone could shed some light on my problem, I would be very grateful.

[bradgrafelman]

$dbc isn't defined within the checkFilmExists() function. (Hint: functions have their own variable scope; read this manual page if you don't understand what that means: [man]variables.scope[/man]).

Common way to solve this would be to pass the $dbc variable to the function as a parameter (global variables aren't considered good coding practice).

[agk]

Brad, thank you! I hadn't realised it until you spelled it out for me, but in every other function I've got:

 global $dbc; 

This is my new code:

function checkFilmExists($dbc, $id)
{
    $q = 'SELECT COUNT(*) FROM movielist WHERE movie_id = '.$id;
    $r = mysqli_query($dbc, $q);
    //echo 'var_dump: ' . var_dump($dbc);
    $row = mysqli_fetch_array($r);
    if($row['COUNT(*)'] == 1)
    {
        return true;
    }
    else
    {
        echo 'Query that didn\'t work: ' . $q;
        return false;
    }
}

if( (isset($_GET['id'])) && (is_numeric($_GET['id'])) && (checkFilmExists($dbc, $_GET['id'])) )
{
    $id = $_GET['id'];
    $filmInfo = getFilmInfo($id);
    $error = false;
}
else
{
    $error = true;
}

And of course it's working properly now. I'll have to see about improving my coding practices throughout the rest of my project.