Question

我尝试使用std :: distance这样：

vi::iterator frontIter = resVec.begin();
vi::reverse_iterator backIter = resVec.rbegin();    

if(std::distance(frontIter , backIter))
{
    std::cout << " ! " << std::endl;
}

但是编译器给了我这个错误。

partion.cpp:46:39: note: candidate is:
In file included from /usr/include/c++/4.9/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/4.9/vector:60,
                 from test.h:1,
                 from partion.cpp:1:
/usr/include/c++/4.9/bits/stl_iterator_base_funcs.h:114:5: note: template<class _InputIterator> typename std::iterator_traits<_Iterator>::difference_type std::distance(_InputIterator, _InputIterator)
     distance(_InputIterator __first, _InputIterator __last)
     ^
/usr/include/c++/4.9/bits/stl_iterator_base_funcs.h:114:5: note:   template argument deduction/substitution failed:
partion.cpp:46:39: note:   deduced conflicting types for parameter ‘_InputIterator’ (‘__gnu_cxx::__normal_iterator<int*, std::vector<int> >’ and ‘std::reverse_iterator<__gnu_cxx::__normal_iterator<int*, std::vector<int> > >’)
  if(std::distance(frontIter , backIter))

所以我如何找到这两个迭代器之间的距离。更好的是，有没有办法解决这个问题而不使用back_iterator，而是使用两个标准迭代器？

for(size idx = 0 ; idx < vec.size() ; ++idx)
{
    if(idx == n) 
    {
        continue;
    }   

    if(vec[idx] < partVal) // insert in front of  partVal
    {

        *frontIter = vec[idx];
        ++frontIter;    
    }
    else // insert at back of n
    {
        *backIter = vec[idx];   
        ++backIter;
    }

}

注意：

using vi = std::vector<int>;
using size = std::size_t;

Answer 1

任何reverse iterator都可以通过base()转换为其基础前向迭代器。

所以你想要的是：

std::distance(v.begin(), v.rbegin().base())

这会给你与v.size()相同的结果。

如何计算std :: vector <int> :: iterator和std :: vector <int> :: reverse_iterator之间的距离？

1 个答案: