I have the followin vector:

```
std::vector<std::pair<std::function<void(iter_type, iter_type)>, bool>> functionList;

```

and at some point, a code is doing:

```
functionList[index].second = enable;

```

which is causing a crash

How can I safely verify if there's an object in this `index` so I can modify?

<https://en.cppreference.com/w/cpp/container/vector/operator_at> says that `operator[]` returns a reference, but I tried to check it for null and couldn't.

Also, what does `reference` means in `reference operator[]( size_type pos );`? Certainly not the same as `&`