multithreading - C++ std::map - thread safe if one thread writes and another reads with always different keys? -

this question has answer here:

• can access c++11 std::map entry while inserting/erasing thread? 4 answers

thread writes std::map key c

thread b reads std::map key d

if guaranteed keys not overlap, thread safe?

since std::map uses tree-structure inside, imagine there problems read while being mutated.

if std::map not work, std::unordered_map better?

• if writing mean changing value of already existing entry associated key c, answer (i believe) yes.
• if writing mean (potentially) inserting new elements (or removing them), answer definitively no.

although not authoritative source, www.cplusplus.com has section potential data races each function.