MSVC编译器错误导致迭代器和朋友函数错误？

Question

我一直在进行小规模的测试，看看我是否可以用更大的容器找出一些特定于编译器的大规模问题。以下代码在GCC中正常工作但在Visual Studio 2010和2013中导致以下错误代码：

“错误1错误C2675：一元' - '：'std :: iterator'未定义此运算符或转换为预定义运算符可接受的类型d：\ programming \ workspaces \ adl_test \ main.cpp 127 1 adL_test_msvc“

测试代码如下：

#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;
}

显然， - 运算符在迭代器上工作正常，如代码所示，但是当从reverse_iterator调用时，MSVC会产生错误，尽管reverse_iterator是朋友。为什么？ 这个bug的解决方法是什么？

不建议使用不同的方式来接近代码（即直接修改i而不是调用 - 运算符），这是测试用例，而不是实际的工作代码。它并不代表实际代码的复杂性，我不会向您解释为什么实际代码以这种方式工作，因为我没有时间。

Answer 1

感谢immibus，我们找到了答案： GCC相信＆＃39; iterator＆＃39;在reverse_iterator中引用test_container :: iterator，而（由于某种原因）MSVC 2010-2013认为它引用了基类。 在reverse_iterator中指定迭代器时，解决方案更具体 - 使用＆＃34; typename test_container :: iterator＆＃34;而不是＆＃34;迭代器＆＃34;。

更正后的代码：

#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: 
        typename test_container::iterator it;

    public: 

        reverse_iterator(element_type &_i)
        {
            it.i = _i;
        }

        reverse_iterator(const typename test_container::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 typename test_container::iterator &source)
        {
            it = source;
            return *this;
        }

        bool operator != (const typename test_container::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;
}