Question

Basically I want to reverse iterate through 2 std::vectors.
a layer has a vector of shapes.

usually I could do something like this:

for(int i = 0; i < layers.size(); ++i)
{
   for(int j = 0; j < layers[i].shapes.size(); ++j)
   {
      layers[i].shapes[j].dosomething();
   }
}

However right now I need to reverse iterate through the vectors and therefore need to use a reverse iterator but how would this work? Since iterators kind of make it like a for each, how can I acces the current shape of the current layer being iterated through?
Thanks

Answer 1

The easy way:

for(int i = layers.size() - 1; i >= 0; --i)
{
   for(int j = layers[i].shapes.size() - 1; j >= 0; --j)
   {
      layers[i].shapes[j].dosomething();
   }
}

The “proper” way:

for(vector<Layer>::reverse_iterator i = layers.rbegin(); i != layers.rend(); ++i)
{
   for(vector<Shape>::reverse_iterator j = i->shapes.rbegin(); j != i->shapes.rend(); ++j)
   {
      j->dosomething();
   }
}