Undefined offset with Internet explorer

I have the same problem in Internet Explorer 11, the red warning shown.
Your code suggestion fixed the problem. I hope this can be included in the next release.

Thanks a lot.

This is Philix's recommendations with some changes to the last part which shouldn't change how it works.

1. Recently in logs I have found few weird sessions from clients without HTTP_USER_AGENT set in $_SERVER. So for this use case I believe it is reasonable to change 4 line from
$user_agent = $_SERVER['HTTP_USER_AGENT'];
to
$user_agent = array_key_exists('HTTP_USER_AGENT', $_SERVER) ? $_SERVER['HTTP_USER_AGENT'] : 'Unknown';

2. There were few sessions with following HTTP_USER_AGENT:
'Mozilla/4.0 (compatible;HostTracker/2.0;+http://www.host-tracker.com/)'
'Mozilla/5.0 (compatible; Baiduspider/2.0; +http://www.baidu.com/search/spider.html)'

So I reckon there will always be a case when we got same Undefined offset: 1 in counter_get_browser() notice.

In order to eliminate this I changed the condition to:

  if ( $ub != 'Unknown' ) {
    if ($i != 1) {
      //we will have two since we are not using 'other' argument yet
      //see if browser_version is before or after the name
      if (strripos($user_agent,"browser_version") < strripos($user_agent,$ub)){
        $browser_version= $matches['browser_version'][0];
      }
      else {
        $browser_version= $matches['browser_version'][1];
      }
    }
    else {
    $browser_version= $matches['browser_version'][0];
    }
  }

I have attached a patch file combined with the previous patch in this issue.

Notice: Undefined offset: 1 in counter_get_browser()

Notice: Undefined offset: 1 in counter_get_browser() (line 76 of /.../sites/all/modules/counter/counter.lib.inc). This error ocurs only with Internet Explorer 11 but not with older versions. The error is not associated with Chrome and Firefox browsers.

Follow the following steps: Navigate to counter.lib.inc through /.../sites/all/modules/counter/counter.lib.inc and open counter.lib.inc on your editor as to edit the file as follows:

After this:

{
$browser_name = 'Internet Explorer';
$ub = "IE";
}

Add this:

elseif(preg_match('/rv:/i',$user_agent))
{
$browser_name = 'Internet Explorer';
$ub = "rv";
}

After this:

// finally get the correct browser_version number
$known = array('browser_version', $ub, 'other');
$pattern = '#(?' . join('|', $known) .
')+(?*)#';

Add this:

if ($ub == 'rv') $pattern = '#(?' . join('|', $known) . ')+(?*)#';

The above procedure gets the issue resolved. For more info, go to: https://www.myniceitems.com/content/notice-undefined-offset-1-counterget...

#5 did not work for me. Getting errors:
Warning: preg_match_all() [function.preg-match-all]: Compilation failed: unrecognized character after (? or )?- at offset 2 in counter_get_browser() (line 65 of ../counter.lib.inc)

Trying out #3 now.

I notice there are multiple errors in the current release, any chance we can get a new roll out with some of the patches rolled into it? Thanks!!