c++ map find() to possibly insert(): how to optimize operations?

I'm using the STL map data structure, and at the moment my code first invokes find(): if the key was not previously in the map, it calls insert() it, otherwise it does nothing.

map<Foo*, string>::iterator it;
it = my_map.find(foo_obj);   // 1st lookup

if(it == my_map.end()){
  my_map[foo_obj] = "some value";  // 2nd lookup
}else{
  // ok do nothing.
}

I was wondering if there is a better way than this, because as far as I can tell, in this case when I want to insert a key that is not present yet, I perform 2 lookups in the map data structures: one for find(), one in the insert() (which corresponds to the operator[] ).

Thanks in advance for any suggestion.