如果成功则返回 TRUE，失败则返回 FALSE。
ldap_free_result() frees up the memory allocated internally to store the result and pointed by the result_identifier. All result memory will be automatically freed when the script terminates.
Typically all the memory allocated for the ldap result gets freed at the end of the script. In case the script is making successive searches which return large result sets, ldap_free_result() could be called to keep the runtime memory usage by the script low.