++it or it++ when iterating over a map?

Question

Examples showing how to iterate over a std::map are often like that:

MapType::const_iterator end = data.end(); 
for (MapType::const_iterator it = data.begin(); it != end; ++it)

i.e. it uses ++it instead of it++. Is there any reason why? Could there be any problem if I use it++ instead?

Answer 1

it++ returns a copy of the previous iterator. Since this iterator is not used, this is wasteful. ++it returns a reference to the incremented iterator, avoiding the copy.

Please see Question 13.15 for a fuller explanation.