Книга: Standard Template Library Programmer

back_insert_iterator

back_insert_iterator<BackInsertionSequence>

Categories: iterators, adaptors

Component type: type

Back_insert_iterator is an iterator adaptor that functions as an Output Iterator: assignment through a back_insert_iterator inserts an object after the last element of a Back Insertion Sequence. [1]

list<int> L;
L.push_front(3);
back_insert_iterator<list<int> > ii(L);
*ii++ = 0;
*ii++ = 1;
*ii++ = 2;
copy (L.begin(), L.end(), ostream_iterator<int>(cout, " "));
// The values that are printed are 3 0 1 2

Defined in the standard header iterator, and in the nonstandard backward-compatibility header iterator.h.

Output Iterator. An insert iterator's set of value types (as defined in the Output Iterator requirements) consists of a single type: BackInsertionSequence::value_type.

The template parameter BackInsertionSequence must be a Back Insertion Sequence.

None.

These members are not defined in the Output Iterator requirements, but are specific to back_insert_iterator.

[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)).

insert_iterator, front_insert_iterator, Output Iterator, Back Insertion Sequence, Sequence, Iterator overview

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