I was converting LDAP related code to PHP7 which doesn't support /e modifier with preg_replace anymore, but instead you should use preg_replace_callback. This might help someone working on the same thing:

<?php

$value = 'Universität';

# < PHP7 compatible code
echo preg_replace("/\\\([0-9A-Fa-f]{2})/e", "''.chr(hexdec('\\1')).''", $value);

# >= PHP7 compatible code
echo preg_replace_callback('/\\\([0-9A-Fa-f]{2})/', function ($matches) { return chr(hexdec($matches[1])); }, $value);

Keep attention on UTF8 encoded DNs. Since openLDAP >=2.1.2
ldap_explode_dn turns unprintable chars (in the ASCII sense, UTF8
encoded) into \<hexcode>.

Example:

$dn="ou=Universität ,c=DE";
var_dump(ldap_explode_dn($dn,0));

//returns

array(3) {
  ["count"]=>
  int(2)
  [0]=>
  string(19) "ou=Universit\C3\A4t"
  [1]=>
  string(4) "c=DE"
}

Unfortunately, PHP don't support the ldap functions ldap_str2dn and 
ldap_dn2str, but by means of preg_replace a workaround is possible to
recover the old behaviour of ldap_explode_dn

// workaround
function myldap_explode_dn($dn,$with_attribute){

$result=ldap_explode_dn ($dn, $with_attrib);
 //translate hex code into ascii again
    foreach($result as $key=>$value){
          $result[$key]=preg_replace("/\\\([0-9A-Fa-f]{2})/e", "''.chr(hexdec('\\1')).''", $value);
    }
    return($result);

}
//
//then follows for the example

$dn="ou=Universität ,c=DE";
var_dump(myldap_explode_dn($dn,0));

//returns

array(3) {
  ["count"]=>
  int(2)
  [0]=>
  string(15) "ou=Universität"
  [1]=>
  string(4) "c=DE"
}

I came accros this page and enjoyed the comments. 

Since a LDAP string can sometimes be lengthy and have many attributes, I needed to be able to sort through all that is in.

In my case, I needed to get the subdomain part and other parameters. 

Here is how I built my method.
<?php
    /**
     * Parse, and format a DN string to Array
     *
     * Read a LDAP DN, and return an array keys
     * listing all similar attributes.
     *
     * Also takes care of the character escape and unescape
     *
     * Example:
     * CN=username,OU=UNITNAME,OU=Region,OU=Country,DC=subdomain,DC=domain,DC=com
     *
     * Would normally return:
     * Array (
     *     [count] => 9
     *     [0] => CN=username
     *     [1] => OU=UNITNAME
     *     [2] => OU=Region
     *     [5] => OU=Country
     *     [6] => DC=subdomain
     *     [7] => DC=domain
     *     [8] => DC=com
     * )
     *
     * Returns instead a manageable array:
     * array (
     *     [CN] => array( username )
     *     [OU] => array( UNITNAME, Region, Country )
     *     [DC] => array ( subdomain, domain, com )
     * )
     *
     *
     * @author gabriel at hrz dot uni-marburg dot de 05-Aug-2003 02:27 (part of the character replacement)
     * @author Renoir Boulanger
     * 
     * @param  string $dn          The DN
     * @return array
     */
    function parseLdapDn($dn)
    {
        $parsr=ldap_explode_dn($dn, 0);
        //$parsr[] = 'EE=Sôme Krazï string';
        //$parsr[] = 'AndBogusOne';
        $out = array();
        foreach($parsr as $key=>$value){
            if(FALSE !== strstr($value, '=')){
                list($prefix,$data) = explode("=",$value);
                $data=preg_replace("/\\\\\\([0-9A-Fa-f]{2})/e", "''.chr(hexdec('\\\\1')).''", $data);
                if(isset($current_prefix) && $prefix == $current_prefix){
                    $out[$prefix][] = $data;
                } else {
                    $current_prefix = $prefix;
                    $out[$prefix][] = $data;
                }
            }
        }
        return $out;
    }
?>

Probably not the best way but for those who are looking for a way to get de CN of a DN without the "cn=" part this is a function with a regex pattern:

<?php
    function getCNofDN($dn) {
        $return=preg_match('/[^cn=]([^,]*)/i',$dn,$dn);
        return($dn[0]);
    }

  echo getCNofDN("cn=emepese,cn=someLevel,dc=someCompany");

// Will print "emepese"

?>

[ Editor's Note: The segfault has been fixed and will not occur in PHP 4.3.4 or PHP 5.0.0 when they are released.  However, it is still important to escape special characters as detailed below. ]

If your DN contains < or > characters, you must escape them with a backslash or ldap_explode_dn() will give you a "wrong parameter count" error or even a segmentation fault.

For example, these calls will fail with a "wrong parameter count" or a seg fault:

  ldap_explode_dn( "cn=<bob>,dc=example,dc=com", 0 );
  ldap_explode_dn( 'cn=<bob>,dc=example,dc=com', 0 );

But this will succeed

  ldap_explode_dn( "cn=\<bob\>,dc=example,dc=com", 0 );

Notice also that the < and > are escaped with hex codes as noted above. This function is a nice wrapper that properly formats all DNs and can safely be called with < and > characters, and UTF-8 characters:

function my_explode_dn( $dn, $with_attributes=0 )
{
        $dn = addcslashes( $dn, "<>" );
        $result = ldap_explode_dn( $dn, $with_attributes );
        //translate hex code into ascii again
        foreach( $result as $key => $value )
                $result[$key] = preg_replace("/\\\([0-9A-Fa-f]{2})/e", "''.chr(hexdec('\\1')).''", $value);
        return $result;
}

I am using php 4.3.1. Good luck!

Copying is much better than typing!!!!
Just modify the constants.
Best wishes (and thanX 4 this helpfull site),
Bernd Schwaegerl
Mueller-Knoche GmbH, Systemhaus fuer EDV-Loesungen

# Example:

$HOST = "Yourhostname";
$USER_DN = "Yourldapuser_dn";
$PWD = "Ldapuserpassword";
$BASE_DN = "o=Your_organisation";
$SEARCH_OBJECT="sn=YOUR_SEARCH_PERSON_OBJECTS_SN";

$ldap_handle=ldap_connect($HOST);
$bind_result=ldap_bind($ldap_handle,$USER_DN,$PWD);

$search_result=ldap_search($ldap_handle,$BASE_DN,$SEARCH_OBJECT);
$result=ldap_get_entries($ldap_handle,$search_result);
$result_array=ldap_get_entries($ldap_handle,$result);
$whole_dn=$result_array[0]["dn"];

$dn_parts=ldap_explode_dn($whole_dn,0);