$_SERVER['HTTP_HOST'] as a variable

[JackTheKnife]

What is different between:

 

$host  = $_SERVER['HTTP_HOST'];

 

and

 

$host = "www.my-domain.com";

 

Somehow when I have to use first line then $_SESSION vars doesn't go through two different domains.

[jake2891]

you can use it for a dev or live environment. or if your writing a reusable piece of code where the host may change.

[JackTheKnife]

Once again, because looks like ppl are confused what I am asking about.

 

I have piece of code:

 

//$host  = $_SERVER['HTTP_HOST']; //disabeld for testing
$host = "www.my-domain.com"; //dummy domain for testing 

$sql = "SELECT * FROM Items WHERE  LandingPageURL = '".$host."'";
               .......
	$landingpage = $row["LandingPage"];
               ...........

if ($landingpage==$host){
	$_SESSION["pid"] = $product['id'];
	$_SESSION["price"] = $product['price'];
               ...........
}
else {
	echo "oops... wrong page";
}

 

Then I do POST form to the another site (domain) on this same server but all $_SESSION vars are empty when I have use $host  = $_SERVER['HTTP_HOST'] instead of $host = "www.my-domain.com";