back_insert_iterator(BackInsertionSequence& S) | Constructs a back_insert_iterator that inserts objects after the last element of S. (That is, it inserts objects just before S's past-the-end iterator.) |
template<class BackInsertionSequence> back_insert_iterator<BackInsertionSequence> back_inserter(BackInsertionSequence& S); | Equivalent to back_insert_iterator<BackInsertionSequence> (S). [3] This is a global function, not a member function. |
Notes [1] Note the difference between assignment through a BackInsertionSequence::iterator and assignment through a back_insert_iterator<BackInsertionSequence>. If i is a valid BackInsertionSequence::iterator, then it points to some particular element in the back insertion sequence; the expression *i = t replaces that element with t, and does not change the total number of elements in the back insertion sequence. If ii is a valid back_insert_iterator<BackInsertionSequence>, however, then the expression *ii = t is equivalent, to the expression seq.push_back(t). That is, it does not overwrite any of seq's elements and it does change seq's size.
[2] Note how assignment through a back_insert_iterator is implemented. In general, unary operator* must be defined so that it returns a proxy object, where the proxy object defines operator= to perform the insert operation. In this case, for the sake of simplicity, the proxy object is the back_insert_iterator itself. That is, *i simply returns i, and *i = t is equivalent to i = t. You should not, however, rely on this behavior. It is an implementation detail, and it is not guaranteed to remain the same in future versions.
[3] This function exists solely for the sake of convenience: since it is a non-member function, the template parameters may be inferred and the type of the back_insert_iterator need not be declared explicitly. One easy way to reverse a range and insert it at the end of a Back Insertion Sequence S, for example, is reverse_copy(first, last, back_inserter(S)) .
See also insert_iterator, front_insert_iterator, Output Iterator, Back Insertion Sequence, Sequence, Iterator overview
insert_iterator<Container>
Categories: iterators, adaptors
Component type: type
Description Insert_iterator is an iterator adaptor that functions as an Output Iterator: assignment through an insert_iterator inserts an object into a Container. Specifically, if ii is an insert_iterator, then ii keeps track of a Container c and an insertion point p; the expression *ii = x performs the insertion c.insert(p, x). [1]
There are two different Container concepts that define this expression: Sequence, and Sorted Associative Container. Both concepts define insertion into a container by means of c.insert(p, x), but the semantics of this expression is very different in the two cases.
For a Sequence S, the expression S.insert(p, x) means to insert the value ximmediately before the iterator p. That is, the two-argument version of insert allows you to control the location at which the new element will be inserted. For a Sorted Associative Container, however, no such control is possible: the elements in a Sorted Associative Container always appear in ascending order of keys. Sorted Associative Containers define the two-argument version of insert as an optimization. The first argument is only a hint: it points to the location where the search will begin.
If you assign through an insert_iterator several times, then you will be inserting several elements into the underlying container. In the case of a Sequence, they will appear at a particular location in the underlying sequence, in the order in which they were inserted: one of the arguments to insert_iterator's constructor is an iterator p, and the new range will be inserted immediately before p.
In the case of a Sorted Associative Container, however, the iterator in the insert_iterator's constructor is almost irrelevant. The new elements will not necessarily form a contiguous range; they will appear in the appropriate location in the container, in ascending order by key. The order in which they are inserted only affects efficiency: inserting an already-sorted range into a Sorted Associative Container is an O(N) operation.
Example Insert a range of elements into a list.
list <int> L;
L.push_front(3);
insert_iterator<list<int> > ii(L, L.begin());
*ii++ = 0;
*ii++ = 1;
*ii++ = 2;
copy(L.begin(), L.end(), ostream_iterator<int>(cout, ' '));
// The values that are printed are 0 1 2 3.
Merge two sorted lists, inserting the resulting range into a set. Note that a set never contains duplicate elements.
int main() {
const int N = 6;
int A1[N] = {1, 3, 5, 7, 9, 11};
int A2[N] = {1, 2, 3, 4, 5, 6};
set<int> result;
merge (A1, A1 + N, A2, A2 + N,
inserter(result, result.begin()));
copy(result.begin(), result.end(), ostream_iterator<int>(cout, ' '));
cout << endl;
// The output is '1 2 3 4 5 6 7 9 11'.
}
Definition Defined in the standard header iterator, and in the nonstandard backward-compatibility header iterator.h.
Template parameters 
