PHP获取客户端IP地址函数（兼容多种情况）

function get_client_ip() {
    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);
}