[ndnSIM] How to get erased item of Content Store

[Maziar]

Hi,

I am trying to get the prefix of the item which has been replaced in 
content store.
What I know so far is that the below command does erasing:
base_.erase (&(*policy_container::begin ()));
But I can not retrieve the prefix of the item from 
policy_container::begin ().

I would appreciate if you help me.

Thanks
Maz