C++ Custom iterator class - c++

Question

I want to implement a custom iterator class that has some differences with typical iterators. The container in this example is a vector and the idea is to walk throw it but using a specific syntax, like this:
int main()
{
VectorElement E;
for (size_t i = 0; i < 5; i++)
{
Element e;
e.id = i;
E.push_back(e);
}
for (ElementIterator e(E); e.end(); ++e)
cout << "Element " << e.id << endl;
}
I tried with the following definitions, but it gives me a Segmentation Fault at the static_cast line after two iterations. Does someone know how to improve this? Thanks
class Element
{
public:
Element() {};
size_t id;
};
typedef vector<Element> VectorElement;
class ElementIterator: public Element
{
typedef vector<Element>::iterator iter;
public:
ElementIterator(const Element& e) : Element(e) { }
ElementIterator(VectorElement& ve_)
{
ve = &ve_;
it = ve->begin();
}
ElementIterator operator++()
{
++it;
*this = static_cast<ElementIterator>(*it);
return *this;
}
bool end()
{
if (it != ve->end() )
return true;
return false;
}
vector<Element>* ve;
iter it;
};

Answer 1

Here is alternate implementation that does not rely on global variables or deriving from 'Element':
class Element
{
public:
Element() {};
size_t id;
};
class ElementIterator
{
std::vector<Element>& ve;
std::vector<Element>::iterator it;
public:
ElementIterator(std::vector<Element>& ve_) : ve(ve_)
{
it = ve.begin();
}
ElementIterator(const ElementIterator &rhs) : ve(rhs.ve)
{
it = rhs.it;
}
ElementIterator operator++()
{
++it;
return *this;
}
const Element *operator ->() const
{
assert(!this->end());
return &(*it);
}
bool end() const
{
if (it == ve.end())
return true;
return false;
}
};
Main:
int main()
{
std::vector<Element> E;
for (size_t i = 0; i < 5; i++)
{
Element e;
e.id = i;
E.push_back(e);
}
for (ElementIterator e(E); !e.end(); ++e)
std::cout << "Element " << e->id << std::endl;
}
NOTE: I changed the behaviour of 'ElementIterator::end' so that it returns 'true' when it is at the end which seemed more logical.
Try it here:
http://coliru.stacked-crooked.com/a/8bf8b1025d87a882

Answer 2

I suspect that the segfault occurs because the 'ElementIterator::operator++()' increments the internal 'it' attribute and then deferences it without verifying that its valid first. It could be implemented as follows:
ElementIterator::operator ++()
{
++it;
if (!this->end())
*this = static_cast<ElementIterator>(*it);
return *this;
}

Answer 3

I finally use this workaround, that it is not elegant but works. The main problem was that the iterator "it" was overwritten so I put it in the global scope.
class Element
{
public:
Element() {};
size_t id;
};
typedef vector<Element> VectorElement;
typedef vector<Element>::iterator iter;
iter it;
class ElementIterator: public Element
{
public:
ElementIterator(const Element& e) : Element(e) { }
ElementIterator(VectorElement& ve_)
{
ve = &ve_;
it = ve->begin();
}
ElementIterator operator++()
{
++it;
*this = static_cast<ElementIterator>(*it);
return *this;
}
bool end()
{
if (it != ve->end() )
return true;
return false;
}
vector<Element>* ve;
};