Non-Object Errors using PHP PDO with MySQL

Question

I've been scratching my head over this for a few days now and I've still got nowhere. I'm trying to pull a small set of values from a MySQL database via PHP PDO; I know PDO works as I am using it else where and I have based my code around te previously working code.

function custom_sub_cat_list($db_details, $cat_id) { //ln21
$subcat = NULL;
try {
    $h = new PDO("mysql:host=".$db_details['host'].";dbase=".$db_details['db'],$db_details['user'],$db_details['pass']);
    $h->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
} catch(PDOException $ex) {
    return false;
}
try {
    $q = $h->prepare("SELECT category FROM :tbl WHERE parentid = :catid;");
    $q->bindValue(":tbl", $db_details['tbl'], PDO::PARAM_STR);
    $q->bindValue(':catid', $cat_id, PDO::PARAM_STR);
    $q->execute();
    while($row = $_query->fetch()) {
        $subcat['id'][] = $row['categoryid'];
        $subcat['name'][] = $row['category'];
    };
    return $subcat;
} catch(PDOException $ex) {
    return false;
}
}//ln49

I am getting "Call to a member function bindValue() on a non-object" on the bindValue's and being called up like below.

$cat_id     = 123;
$db_details = array(
    "host"  => $sql_host,
    "db"    => $sql_db,
    "user"  => $sql_user,
    "pass"  => $sql_password,
    "tbl"   => $sql_tbl['categories']
);
custom_sub_cat_list ($db_details, $cat_id)

I'm sure it's something glaringly obvious but I can't see the problem and would like a fresh pair of eyes.

WORKING VERSION BELOW

Thank You Very Very Much! to everyone who helped, I've learnt a few bits too :-) There was some silly mistakes in there that I had overlooked, I just blame looking at it for two days solid.

function custom_sub_cat_list($db_details, $cat_id) {
$subcat = NULL;
try {
    $h = new PDO("mysql:host=".$db_details['host'].";dbname=".$db_details['db'].";charset=utf8",$db_details['user'],$db_details['pass']);
    $h->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
    $h->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $q = $h->prepare("SELECT category, categoryid FROM ".$db_details['table']." WHERE parentid = :cid;");
    $q->bindParam(':cid', $cat_id, PDO::PARAM_INT);
    $q->execute();
    while($row = $q->fetch()) {
        $subcat['id'][] = $row['categoryid'];
        $subcat['name'][] = $row['category'];
    };
    $h = NULL;
    return $subcat;
} catch(PDOException $ex) {
    print_r($ex->getMessage());
    print_r($ex->getTrace());
    //return false;
}
}

Answer 1

You don't need a fresh pair of eyes

You are not painter but a programmer (supposedly).
So, instead of watching your code you have to run it. And enable error reporting.

Oh, just spotted it
And of course, you shouldn't gag error messages!

} catch(PDOException $ex) {
    return false;
}

a modern version of @ operator.
Please get rid of ALL try..catch blocks in your code and start using them only after learning what are they for.

So, in order to solve this very problem as well as many other problems in the future

1. Get rid of all try..catch blocks in your code.
2. Enable error reporting for PDO as described in tag wiki I linked to in the comments.
3. Do not use placeholders for the identifiers but format them as described in the tag wiki I linked to
4. Turn off display_errors setting if you don't want errors to be displayed (the only reason for suppressing error messages I can think of).

Also, you shouldn't open separate connection in every function call.
Create one connection in the beginning of your script and then use if in the function, using

global $h;