Copy std::map data to another map

Copying one map to another can be done with operator = or the copy constructor.

E.g

map<X, Y> mp1; 
//fill mp1 with data
map<X, Y> mp2(mp1); //mp2 is a copy of mp1 (via copy-construction)
map<X, Y> mp3;
mp3 = mp2; // mp3 is also a copy of mp2 (via copy-assignment)