The behavior of overlapped vector::insert.

Question

Where does the C++ standard declare that the pair of iterators passed to std::vector::insert must not overlap the original sequence?

Edit: To elaborate, I'm pretty sure that the standard does not require the standard library to handle situations like this:

std::vector<int> v(10);
std::vector<int>::iterator first = v.begin() + 5;
std::vector<int>::iterator last = v.begin() + 8;
v.insert(v.begin() + 2, first, last);

However, I was unable to find anything in the standard, that would prohibit the ranges [first, last) and [v.begin(), v.end()) to overlap.

Answer 1

Consider the behavior if it was allowed. Every insert into the vector would both increase the distance between the start and end iterator by one and move the start iterator up one. Therefore the start iterator would never reach the end iterator and the algorithm would execute until an out of memory exception occurred.

Answer 2

23.1.1/4 Sequence requirements has:

expression: a.insert(p,i,j)

return type: void

precondition: i,j are not iterators into a. inserts copies of elements in[i,j) before p.

So i and j cannot be iterators into your vector.

It makes sense, as during the insert operation, the vector may need to resize itself, and so the existing elements may first be copied to a new memory location (there by invalidating the current iterators).