c++ - Using my custom iterator with stl algorithms

I'm trying to create my own iterator, and I've got it working as expected with the std::generate algorithm. However, when I try std::max_element of std::find, I get some cryptic errors.

Here is the interface for my iterator:

template           typename GridPtr,
          typename GridRef,
          template  class ShapeT>
class GridIterator
{
public:
    typedef GridIterator Iterator;


    // Iterator traits - typedefs and types required to be STL compliant
    typedef std::ptrdiff_t           difference_type;
    typedef typename GridT::Element  value_type;
    typedef typename GridT::Element* pointer;
    typedef typename GridT::Element& reference;
    typedef size_t                   size_type;
    std::forward_iterator_tag        iterator_category;



    GridIterator(GridT& grid,
                 ShapeT shape,
                 Index iterStartIndex);

    ~GridIterator();

    Iterator& operator++();
    Iterator  operator++(int);

    typename GridT::Element& operator*();

    typename GridT::Element* operator->();

    bool operator!=(const GridIterator& rhs) const;
    bool operator==(const GridIterator& rhs) const; 
    ....

}

Using std::find, I get this error

In file included from /usr/include/c++/4.6/algorithm:63:0,
from ./grid/Map_Grid.h:11,
from main.cpp:4: /usr/include/c++/4.6/bits/stl_algo.h: In function ‘_IIter
std::find(_IIter, _IIter, const _Tp&) [with _IIter =
Map::GridIterator, Map::Grid*,
Map::Grid&, Map::Rectangle>, _Tp = int]’:
main.cpp:103:50: instantiated from here
/usr/include/c++/4.6/bits/stl_algo.h:4404:45: error: no matching

function for call to
‘__iterator_category(Map::GridIterator,
Map::Grid*, Map::Grid&, Map::Rectangle>&)’
/usr/include/c++/4.6/bits/stl_algo.h:4404:45: note: candidate is:
/usr/include/c++/4.6/bits/stl_iterator_base_types.h:202:5: note:
template typename std::iterator_traits::iterator_category
std::__iterator_category(const _Iter&)

With std::max_element :

In file included from /usr/include/c++/4.6/bits/char_traits.h:41:0,
from /usr/include/c++/4.6/ios:41,
from /usr/include/c++/4.6/ostream:40,
from /usr/include/c++/4.6/iostream:40,
from ./grid/Map_GridIterator.h:7,
from ./grid/Map_Grid.h:8,
from main.cpp:4: /usr/include/c++/4.6/bits/stl_algobase.h: In function ‘const _Tp&
std::max(const _Tp&, const _Tp&) [with _Tp =

Map::GridIterator, Map::Grid*,
Map::Grid&, Map::Rectangle>]’: main.cpp:102:60:
instantiated from here /usr/include/c++/4.6/bits/stl_algobase.h:215:7:
error: no match for ‘operator<’ in ‘__a < __b’
/usr/include/c++/4.6/bits/stl_algobase.h:215:7: note: candidates are:
/usr/include/c++/4.6/bits/stl_pair.h:207:5: note: template constexpr bool std::operator<(const std::pair<_T1, _T2>&,
const std::pair<_T1, _T2>&)
/usr/include/c++/4.6/bits/stl_iterator.h:291:5: note: template bool std::operator<(const std::reverse_iterator<_Iterator>&, const
std::reverse_iterator<_Iterator>&)
/usr/include/c++/4.6/bits/stl_iterator.h:341:5: note: template bool std::operator<(const std::reverse_iterator<_IteratorL>&, const
std::reverse_iterator<_IteratorR>&)

/usr/include/c++/4.6/bits/stl_iterator.h:1049:5: note: template bool std::operator<(const std::move_iterator<_IteratorL>&, const
std::move_iterator<_IteratorR>&)
/usr/include/c++/4.6/bits/stl_iterator.h:1055:5: note: template bool std::operator<(const std::move_iterator<_Iterator>&, const std::move_iterator<_Iterator>&)
/usr/include/c++/4.6/bits/basic_string.h:2510:5: note: template bool std::operator<(const std::basic_string<_CharT, _Traits, _Alloc>&, const
std::basic_string<_CharT, _Traits, _Alloc>&)
/usr/include/c++/4.6/bits/basic_string.h:2522:5: note: template bool std::operator<(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*)
/usr/include/c++/4.6/bits/basic_string.h:2534:5: note: template bool std::operator<(const _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&) /usr/include/c++/4.6/bits/stl_vector.h:1290:5: note: template bool std::operator<(const std::vector<_Tp, _Alloc>&, const std::vector<_Tp, _Alloc>&) /usr/include/c++/4.6/tuple:586:5: note: template bool std::operator<(const std::tuple<_TElements
...>&, const std::tuple<_Elements ...>&)

Answer

You are missing a typedef keyword for declaring an alias indicating the iterator category:

// Iterator traits - typedefs and types required to be STL compliant
//...
typedef std::forward_iterator_tag iterator_category;
~~~~~~^

Without the typedef, you are actually declaring a data member.

To avoid such mistakes, you can utilize the std::iterator class template as a base class, instead of defining those aliases on your own:

class GridIterator : public std::iterator                                        , typename GridT::Element>