获取两个文件的相对路径

<?php
$a = "/a/c/d/a.php";
$b = "/a/c/b.php";

function get_relative($a, $b)
{
    $path = '';
    $arr_a = explode('/', $a);
    $arr_b = explode('/', $b);

    $count_a = count($arr_a) - 1;
    $count_b = count($arr_b) - 1;

    $cur = 0;
    while ($cur < $count_a && $cur < $count_b) {
        if ($arr_a[$cur] != $arr_b[$cur]) {
            break;
        }
        $cur++;
    }

    for ($i=$count_b;$i>=0;$i--) {
        if ($i == $cur) {
            break;
        }
        $path .= '../';
    }

    for ($i=$cur;$i<=$count_a;$i++) {
        $path .= sprintf("%s/", $arr_a[$i]);
    }

    $path = rtrim($path, '/');
    
    return $path;
}

echo get_relative($a, $b);

?>