Simple "add query" function that does not use parse_str()

add_query.php

<?php

function add_query($url, $params, $replace = false) {
    $pu = parse_url($url);

    foreach ($params as $k => $v) {
        $np = $k . '=' . urlencode($v);

        if ($replace && preg_match('/(^|&)' . $k . '=/', $pu['query'])) {
            $pu['query'] = preg_replace('/(^|&)' . $k . '=([^&]*)?/', '$1' . str_replace('$', '\$', $np), $pu['query']);
        } else {
            $pu['query'] .= (empty($pu['query']) ? '' : '&') . $np;
        }
    }

    if (strlen($pu['port']) > 0)     $pu['port'] = ':' . $pu['port'];
    if (strlen($pu['query']) > 0)    $pu['query'] = '?' . $pu['query'];
    if (strlen($pu['pass']) > 0)     $pu['user'] .= ':' . $pu['pass'];
    if (strlen($pu['user']) > 0)     $pu['user'] .= '@';
    if (strlen($pu['fragment']) > 0) $pu['fragment'] = '#' . $pu['fragment'];

    return $pu['scheme'] . '://' . $pu['user'] . $pu['host'] . $pu['port'] . $pu['path'] . $pu['query'] . $pu['fragment'];
}

test.php

<?php

$url = 'http://www.example.com/test?test[]=1&stc=bla&test[]=2';
// $url = 'http://www.example.com/test?2';

echo add_query($url, array('stc' => 'hello'), true);