Question

I have a method to which a vector’s iterator is passed.
In this method I’d like to add some elements into the vector, but I am not sure whether this is possible when having only the iterator

void GUIComponentText::AddAttributes(vector<GUIComponentAttribute*>::iterator begin, vector<GUIComponentAttribute*>::iterator end)
{
    for (vector<GUIComponentAttribute*>::iterator i = begin; i != end; ++i)
    {
        GUIComponentAttribute &attrib = *(*i);

        // Here are the GUIComponentAttribute objects analyzed - if an object of a 
        // special kind appears, I would like to add some elements to the vector
    }
}

Thanks
Markus

Answer 1

First, you’ll have to change the interface. Given two iterators,
there’s no way to get back to the container to which they refer; so if
you want to modify the container, you’ll have to pass a reference to it,
i.e.:

void GUIComponentText::AddAttributes(
        std::vector<GUIComponentAttribute*>& attributes )
{
    for ( std::vector<GUIComponentAttribute*>::iter = attributes.begin();
            iter != attributes.end();
            ++ iter )
    {
        //  ...
    }
}

Having done that: insertion can invalidate iterators. So it depends on
where you want to insert. If you want to insert at the current
position: std::vector<>::insert of a single element returns an
iterator to that element, which was inserted before your element, so you
can assign it to your iterator, adjust (if necessary), and continue:

iter = attributes.insert(iter, newAttribute);
++ iter;   //  Return to where we were...

If you’re appending (push_back), the problem is a bit more complex;
you need to calculate the offset, then reconstruct the iterator:

size_t offset = iter - attributes.begin();
attributes.push_back( nweAttribute );
iter = attributes.begin() + offset;

In this case, it is probably simpler to iterate using a size_t and
[], rather than an iterator.