Entry

Why does $HTTP_REFERER return an empty string?

Jun 13th, 2002 12:16
Philip Olson, greg leturk, Richard Lynch, Nathan Wallace,

We'll discuss a few possible reasons:
First, are you trying to use $HTTP_REFERER inside a function? If so, 
you'll need to either add a 'global $HTTP_REFERER' line to your 
function to get at the variable from the global scope or pass it in as 
a argument.  For example :
  function foo()
  {
  global $HTTP_REFERER;
    echo "Referrer is : $HTTP_REFERER";
  }
  http://php.net/manual/language.variables.scope.php
Second, in order for HTTP_REFERER to exist, there needs to be a 
HTTP_REFERER header.  This header does not exist if someone types in 
the URL directly (ie: does not follow a link to the page).  It only 
exists when someone clicks on a link from another page.  And, some 
browsers don't send them.
Thirdly, your server may also be configured to not provide 
$HTTP_REFERER in the first place.  The PHP directive register_globals is
what creates it otherwise it's only available within the
$HTTP_SERVER_VARS and $_SERVER arrays.  register_globals has recently 
been defaulted to off (as of 4.2.0).  So:
  // Worked since PHP 3 (forever)
  print $HTTP_SERVER_VARS['HTTP_REFERER'];
  // Worked since PHP 4.1.0
  print $_SERVER['HTTP_REFERER'];
Fourthly, be sure to check spelling.  You may notice that referrer is 
misspelled as referer in this variable, read a explanation on that 
here :
  http://foldoc.doc.ic.ac.uk/foldoc/foldoc.cgi?query=referer
Lastly, HTTP_REFERER is not passed by some older browsers.
This is a 'predefined variable', read up on it and other such variables 
here:
  http://www.php.net/manual/language.variables.predefined.php