PHP排序多维数组失败

Question

I have this array :

Array
(
    [0] => Array
        (
            [id] => 83
            [value] => Figures
        )

    [1] => Array
        (
            [id] => 85
            [value] => Toys
        )

    [2] => Array
        (
            [id] => 36
            [value] => Nintendo Switch
        )

)

and I have this code to sort that array based on id :

function cmp($a, $b) {
    return strcmp($a->id, $b->id);
}

while ($row = $result->fetch_assoc()) {

    $category = json_decode($row['product_cat'], true);

    usort($category, "cmp");

    echo '<pre>';
    print_r($category);
    echo '</pre>';
}

the result is not working as I expected, because id=85 placed before id=83 :

Array
(
    [0] => Array
        (
            [id] => 36
            [value] => Nintendo Switch
        )

    [1] => Array
        (
            [id] => 85
            [value] => Toys
        )

    [2] => Array
        (
            [id] => 83
            [value] => Figures
        )

)

why PHP successfully placed the id=36 as first value of array, but failed to sort id=85 and id=83

thank you.

Answer 1

change

return strcmp($a->id, $b->id);

to

return strcmp($a['id'], $b['id']);