I've been working on a small-scale test to see if I can figure out some compiler-specific larger-scale problems with a larger container. The following code works fine in GCC but causes the following error code in Visual Studio 2010 and 2013:
"Error 1 error C2675: unary '--' : 'std::iterator' does not define this operator or a conversion to a type acceptable to the predefined operator d:\programming\workspaces\adl_test\main.cpp 127 1 adL_test_msvc"
Test code is as follows:
#include <iostream>
#include <iterator>
namespace nsp
{
template <class element_type, class element_allocator_type = std::allocator<element_type> >
class test_container
{
private:
element_type numbers[50];
friend class iterator;
friend class reverse_iterator;
public:
class reverse_iterator; //forward decl
class iterator : public std::iterator<std::bidirectional_iterator_tag, element_type>
{
private:
element_type *i;
template <class distance_type>
friend void advance(reverse_iterator &rit, distance_type n);
public:
iterator() {}
iterator(element_type &_i)
{
i = &(_i);
}
element_type & operator *()
{
return *i;
}
iterator & operator = (const element_type &source_i)
{
i = &(source_i);
return *this;
}
iterator & operator = (const iterator &source)
{
i = source.i;
return *this;
}
bool operator != (const iterator rh)
{
return i != rh.i;
}
iterator & operator ++()
{
++i;
return *this;
}
iterator & operator --()
{
--i;
return *this;
}
template <class distance_type>
friend void advance(iterator &it, distance_type n)
{
it.i += n;
}
friend typename std::iterator_traits<iterator>::difference_type distance(const iterator &first, const iterator &last)
{
return last.i - first.i;
}
};
class reverse_iterator : public std::iterator<std::bidirectional_iterator_tag, element_type>
{
private:
iterator it;
public:
reverse_iterator(element_type &_i)
{
it.i = _i;
}
reverse_iterator(const iterator &source)
{
it = source;
}
element_type & operator *()
{
return *it;
}
element_type & operator = (const reverse_iterator &source)
{
it = source.it;
return *this;
}
element_type & operator = (const iterator &source)
{
it = source;
return *this;
}
bool operator != (const iterator rh)
{
return it != rh.it;
}
reverse_iterator & operator ++()
{
--it;
return *this;
}
reverse_iterator & operator --()
{
++it;
return *this;
}
template <class distance_type>
friend void advance(reverse_iterator &rit, distance_type n)
{
rit.it.i -= n;
}
friend typename std::iterator_traits<reverse_iterator>::difference_type distance(const reverse_iterator &first, const reverse_iterator &last)
{
return distance(last.it, first.it);
}
};
iterator begin()
{
return iterator(numbers[0]);
}
iterator end()
{
return iterator(numbers[50]);
}
};
}
int main(int argc, char **argv)
{
nsp::test_container<int> stuff;
int counter = 0;
for (nsp::test_container<int>::iterator it = stuff.begin(); it != stuff.end(); ++it)
{
*it = counter++;
}
nsp::test_container<int>::iterator it = stuff.begin(), it2 = stuff.begin();
using namespace std;
std::cout << *it << std::endl;
++it;
--it;
++it;
std::cout << *it << std::endl;
advance(it, 2);
std::cout << *it << std::endl;
std::advance(it, 2);
std::cout << *it << std::endl;
int distance_between = distance(it2, it);
std::cout << distance_between << std::endl;
nsp::test_container<int>::reverse_iterator rit = it, rit2 = it2;
--rit;
++rit;
advance(rit, -2);
distance_between = distance(rit2, rit);
std::cout << distance_between << std::endl;
std::cin.get();
return 0;
}
Obviously the -- operator works fine on iterator as is demonstrated in the code, but when called from reverse_iterator MSVC creates an error, despite reverse_iterator being a friend. Why? And what is the workaround for this bug?
Don't suggest different ways of approaching the code (ie. modifying i directly instead of calling -- operator), this is a test case, not actual working code. It does not represent the complexity of the actual code and I won't explain to you why the actual code works in this way because I don't have time.
