iterator insert(iterator pos,
    const T &x)
 
        Insert x before position pos.
void insert(iterator pos, size_type n,
    const T &x)
 
        Insert n number of elements x before position pos.
void insert(iterator pos, InputIterator first,
    InputIterator last)
 
        Range insertion.
Insert elements in range [first, last) into this vector before position pos.
void insert(iterator pos, const_iterator first,
    const_iterator last)
 
        Range insertion.
Insert elements in range [first, last) into this vector before position pos.
The iterator pos in the functions must be a read-write iterator, can't be read only.