PHP不常见的语法

?? 意思是，判断前面的值是否存在，存在则使用前面的值，不存在，则使用??后面的值。两个问好之间不可以有空格

$res = isset($_GET['name']) ?$_GET['name']: 'long';
$res = $_GET['name'] ?? 'long';

/**
 * Get client ip.
 *
 * @return string
 */
function get_client_ip()
{
    if (!empty($_SERVER['REMOTE_ADDR'])) {
        $ip = $_SERVER['REMOTE_ADDR'];
    } else {
        // for php-cli(phpunit etc.)
        $ip = defined('PHPUNIT_RUNNING') ? '127.0.0.1' : gethostbyname(gethostname());
    }

    return filter_var($ip, FILTER_VALIDATE_IP) ?: '127.0.0.1';
}

/**
 * Get current server ip.
 *
 * @return string
 */
function get_server_ip()
{
    if (!empty($_SERVER['SERVER_ADDR'])) {
        $ip = $_SERVER['SERVER_ADDR'];
    } elseif (!empty($_SERVER['SERVER_NAME'])) {
        $ip = gethostbyname($_SERVER['SERVER_NAME']);
    } else {
        // for php-cli(phpunit etc.)
        $ip = defined('PHPUNIT_RUNNING') ? '127.0.0.1' : gethostbyname(gethostname());
    }

    return filter_var($ip, FILTER_VALIDATE_IP) ?: '127.0.0.1';
}

/**
 * Return current url.
 *
 * @return string
 */
function current_url()
{
    $protocol = 'http://';

    if (!empty($_SERVER['HTTPS']) || ($_SERVER['HTTP_X_FORWARDED_PROTO'] ?? 'http') === 'https') {
        $protocol = 'https://';
    }

    return $protocol.$_SERVER['HTTP_HOST'].$_SERVER['REQUEST_URI'];
}