Standard Template Library Programmer's Guide

[1] Note how assignment through an ostream_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 output operation. In this case, for the sake of simplicity, the proxy object is the ostream_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.

istream_iterator, Output Iterator, Input Iterator.

Categories: iterators, adaptors

Component type: type

Front_insert_iterator is an iterator adaptor that functions as an Output Iterator: assignment through a front_insert_iterator inserts an object before the first element of a Front Insertion Sequence. [1] [2]

list L;

L.push_front(3);

front_insert_iterator > ii(L);

*ii++ = 0;

*ii++ = 1;

*ii++ = 2;

copy(L.begin(), L.end(), ostream_iterator(cout, " "));

// The values that are printed are 2 1 0 3

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

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

The template parameter FrontInsertionSequence must be a Front Insertion Sequence.

None.

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

[1] Note the difference between assignment through a FrontInsertionSequence::iterator and assignment through an front_insert_iterator . If i is a valid FrontInsertionSequence::iterator , then it points to some particular element in the front insertion sequence; the expression *i = t replaces that element with t , and does not change the total number of elements in the sequence. If ii is a valid front_insert_iterator , however, then the expression *ii = t is equivalent, for some FrontInsertionSequence seq , to the expression seq.push_front(t) . That is, it does not overwrite any of seq 's elements and it does change seq 's size.

[2] Note the difference between a front_insert_iterator and an insert_iterator . It may seem that a front_insert_iterator is the same as an insert_iterator constructed with an insertion point that is the beginning of a sequence. In fact, though, there is a very important difference: everyassignment through a front_insert_iterator corresponds to an insertion before the first element of the sequence. If you are inserting elements at the beginning of a sequence using an insert_iterator , then the elements will appear in the order in which they were inserted. If, however, you are inserting elements at the beginning of a sequence using a front_insert_iterator , then the elements will appear in the reverse of the order in which they were inserted.

[3] Note how assignment through an front_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 front_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.

[4] 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 front_insert_iterator need not be declared explicitly. One easy way to reverse a range and insert it at the beginning of a Front Insertion Sequence S , for example, is copy(first, last, front_inserter(S)) .

insert_iterator, back_insert_iterator, Output Iterator, Sequence, Front Insertion Sequence, Iterator overview