What does iterator->second mean?

Question

In C++, what is the type of a std::map<>::iterator?

We know that an object it of type std::map::iterator has

Answer 1

The type of the elements of an std::map (which is also the type of an expression obtained by dereferencing an iterator of that map) whose key is K and value is V is std::pair - the key is const to prevent you from interfering with the internal sorting of map values.

std::pair<> has two members named first and second (see here), with quite an intuitive meaning. Thus, given an iterator i to a certain map, the expression:

i->first

Which is equivalent to:

(*i).first

Refers to the first (const) element of the pair object pointed to by the iterator - i.e. it refers to a key in the map. Instead, the expression:

i->second

Which is equivalent to:

(*i).second

Refers to the second element of the pair - i.e. to the corresponding value in the map.