Output Iterator (iterator)

Definition

Algorithms on input iterators should never attempt to pass through the same iterator twice. They should be single pass algorithms.

Creation

iterator it;

iterator it ( iterator it1);

Operations

iterator&	it = iterator it1	Assignment.
bool	it == iterator it1	Test for equality: Two iterators are equal if they refer to the same item.
bool	it != iterator it1	Test for inequality. The result is the same as !(it == it1).
T&	* it	Returns a reference to the value of the iterator. This operator can only be used in order to assign a value to this reference.
iterator&	++ it	Prefix increment operation. Precondition: it is dereferenceable.
void	it ++	Postfix increment operation. The result is the same as that of iterator tmp = it; ++it; return tmp;. Precondition: it is dereferenceable.

Example

{
    ostream_iterator<double> it(cout);
    for(int r = 0; r < 10; r++){
        *it = 3.1415 * r * r;
        ++it;
    }
}

The above code fragment is equivalent to:

{
    for(int r = 0; r < 10; r++){
        cout << 3.1415 * r * r;  
    }
}

The use of output iterators is better illustrated with a function that can write into arbitrary containers:

template < class OutputIterator >
void
generator(OutputIterator it)
{
    for(int r = 0; r < 10; r++){
        *it = 3.1415 * r * r;
        ++it;
    }
}

and here comes its usage.

{
    ostream_iterator<double> it(cout);
    generator(it);
    double R[10];
    generator(R);
}

Note that the memory where the function generator writes to must be allocated. If you want to insert the generated doubles at the end of a list you have to use a back_insert_iterator. To explain this is out of the scope of this introduction to the STL. Please refer to the STL reference manuals.