PHP 4.3.10
I was trying to do an ldapsearch without a basedn. First, I tried with ' ', as suggested above, but it gave me invalid dn syntax error.
ie:
$sr=ldap_search($ds, ' ', $filter);
Warning: ldap_search(): Search: Invalid DN syntax in ...
Then I changed it to
$sr=ldap_search($ds, "", $filter);
Which gave me the following error:
Warning: ldap_search(): Search: No such object in ...
With that I then modified my ldap.conf file and commented out the BASE field
#BASE dc=example, dc=com
Then it worked!
So it looks like if you supply a blank basedn, then it will use your default basedn in ldap.conf.
