php 获取访问ip方法

if (getenv("HTTP_CLIENT_IP") && strcasecmp(getenv("HTTP_CLIENT_IP"), "unkNown")) {
    $ip = getenv("HTTP_CLIENT_IP");
} else if (getenv("HTTP_X_FORWARDED_FOR") && strcasecmp(getenv("HTTP_X_FORWARDED_FOR"), "unkNown")) {
    $ip = getenv("HTTP_X_FORWARDED_FOR");
} else if (getenv("REMOTE_ADDR") && strcasecmp(getenv("REMOTE_ADDR"), "unkNown"))
    $ip = getenv("REMOTE_ADDR");
else if (isset($_SERVER['REMOTE_ADDR']) && $_SERVER['REMOTE_ADDR'] && strcasecmp($_SERVER['REMOTE_ADDR'], "unkNown"))
    $ip = $_SERVER['REMOTE_ADDR'];
else
    $ip = "unkNown";
return ($ip);