我一直在做一个小规模的测试，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 中工作正常，但在 Visual Studio 2010 和 2013 中会导致以下错误代码：
"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 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，正如代码中所演示的那样，-- 运算符在迭代器上工作正常，但是当从 reverse_iterator MSVC 调用时，尽管reverse_iterator是朋友，但会产生错误。为什么？此错误的解决方法是什么？
不要建议不同的代码处理方式(即直接修改i而不是调用--运算符(，这是一个测试用例，而不是实际的工作代码。它并不代表实际代码的复杂性，我不会向你解释为什么实际代码以这种方式工作，因为我没有时间。
感谢immibus，找到了答案：GCC认为reverse_iterator中的"迭代器"是指test_container：：iterator，而(出于某种原因(MSVC 2010-2013认为它指的是基类。解决方案是在reverse_iterator中指定迭代器时更具体 - 使用"typename test_container：：iterator"而不是"iterator"。
更正的代码：
#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;
}