[Boost-users] How to return a Null pointer for shared_ptr

Hi, I defined a shared_ptr in to a map table. How can I return a NULL pointer in a function to search the table if it is not found as following example? typedef shared_ptr<int> IntPtr; typedef std::map<std::string IntPtr> MapTable; MapTable mt; IntPtr search(const std::string& key) { MapTable::const_iterator it = mt.find(key); if (it == mt.end()) { return NULL; // can't compile it?? } return it->second; } Thank you. Kind regards, Jupiter