preventing undefined index notices

[topr8]

i'm using this snippet of code:

if ($_SERVER["HTTPS"] == "on"){ .... stuff here

and i'm getting a php notice.

eg. Notice: Undefined index: HTTPS in /var/....../filename.php on line 55

how would i avoid this?

i'm getting a similar problem with
if ($_SERVER["HTTP_REFERER"]){

i'm gettign a similar notice,
eg: Undefined index: HTTP_REFERER in ...

any ideas? i know a notice isn't critical but i'd like to keep it tidy.

[Psychopsia]

Hello! The following can work too:

$_SERVER["SERVER_PORT"] === 443

I use this and work fine.

[dreamcatcher]

Use isset [php.net].

if (isset($_SERVER["HTTPS"]) && $_SERVER["HTTPS"] == "on")...

if (isset($_SERVER["HTTP_REFERER"])) {
code here..
}

dc

[topr8]

great, using isset worked, thank you