Question

template <class InputIterator>
    void insert ( iterator position, InputIterator first, InputIterator last );

I need to insert twice into my vector, but the data is large and my vector needs to reallocate. How am I supposed to know where to insert the second time (at the same position) if the call to insert invalidates the iterator?

Am I supposed to do something like this:

int offset = position - vector.begin();
vector.insert(position, data.begin(), data.end());
vector.insert(vector.begin() + offset, moredata.begin(), moredata.end());

It just seems there is a better way.

Answer 1

Er… But you are the only person that knows where you want to insert your data. How is vector supposed to know where you are planning to make the second insertion?

If you plan to make two consecutive insertions at the same location (just guessing), then you can convert your iterator to “reallocation-independent” form (index), and then convert it back to iterator after the first insertion.