STL--iterator

Iterator is a generalization of a pointer.

scores.erase(scores.begin(), scores.begin()+2);

It erases the first and second elements.

old_v.insert(old_v.end(),new_v.begin()+1, new_v.end())

An iterator should have at least 4 properties.

1. dereference *p
2. assign an iterator to another. p=q
3. compare one iterator to another for equality. p ==q and p != q
4. ++p and –p

kind	usage	note
input iterators	read but not alter	a one-way iterator; it can increment, but it can’t back up
output iterators	write but not read	single-pass, write-only
forward iterators	only ++ operators; go forward through a container one element at a time	read and write
bidirectional iterators	++ and –	has all the features of forward iterators
random access iterators	the ability to jump directly to an arbitrary element of a container	a+n; n+a;a[n];a

find() function, by using a lowly input iterator, can be used with any container that contains readable valeus.

sort(） function, by requiring a random access iterator, can be used just with containers that support that kind of iterator.

list doubly linked list, used a bidirectional iterator., it can’t use algorithms base on random access iterators.

STL algorithms can use pointers to operate on non-STL containers that based on pointers.

const int SIZE = 10;
double deceipts[SIZE];
sort(Receipts, Receipts + SIZE);

Reverse pointers solve both problems by decrementing first and then dereferencing. That is, *rp dereferences the iterator immediately preceding the current value of *rp. If rp points to position six, *rp is the value of position five.