When I access an element in [std::unordered\_map using operator []](http://en.cppreference.com/w/cpp/container/unordered_map/operator_at) for the first time, it is automatically created. What (if any) are guarantees about its initialization? (It is guaranteed to be value initialized, or only to be constructed)?

Example:

```
std::unordered_map<void *, size_t> size;
char *test = new char[10];
size[test] += 10;

```

Is size[test] guaranteed to be 10 at the end of this sequence?