vector::insert

iterator insert(iterator it, const T& x);
void insert(iterator it, size_type n, const T& x);
template<class InIt>
    void insert(iterator it, InIt first, InIt last);

Each of the member functions inserts, before the element pointed to by it in the controlled sequence, a sequence specified by the remaining operands. The first member function inserts a single element with value x and returns an iterator that points to the newly inserted element. The second member function inserts a repetition of n elements of value x.

If InIt is an integer type, the last member function behaves the same as insert(it, (size_type)first, (T)last). Otherwise, the last member function inserts the sequence [first, last), which must not overlap the initial controlled sequence.

When inserting a single element, the number of element copies is linear in the number of elements between the insertion point and the end of the sequence. When inserting a single element at the end of the sequence, the amortized number of element copies is constant. When inserting N elements, the number of element copies is linear in N plus the number of elements between the insertion point and the end of the sequence — except when the template member is specialized for InIt an input iterator, which behaves like N single insertions.

If reallocation occurs, the size of the controlled sequence at least doubles, and all iterators and references become invalid. If no reallocation occurs, iterators become invalid only from the point of insertion through the end of the sequence.

If an exception is thrown during the insertion of a single element, the container is left unaltered and the exception is rethrown. If an exception is thrown during the insertion of multiple elements, and the exception is not thrown while copying an element, the container is left unaltered and the exception is rethrown.