反向迭代器不会编译

Question

我正在尝试编译一个反向迭代器但是我这样做的尝试给了一个可怕的混乱.代码的最小例子是......

#include <iostream>
#include <vector>
#include <algorithm>

class frag {
    public:
        void print (void) const;
    private:
        std::vector<int> a;
};

void frag::print (void) const
{
    for (std::vector<int>::reverse_iterator iter = a.begin ();
         iter                                   != a.end ();
         ++iter) {
        std::cout << *iter << std::endl;
    }
}

并尝试编译它产生以下...

In file included from /usr/include/c++/4.4/bits/stl_algobase.h:69,
             from /usr/include/c++/4.4/bits/char_traits.h:41,
             from /usr/include/c++/4.4/ios:41,
             from /usr/include/c++/4.4/ostream:40,
             from /usr/include/c++/4.4/iostream:40,
             from frag.cpp:1:
/usr/include/c++/4.4/bits/stl_iterator.h: In constructor ‘std::reverse_iterator<_Iterator>::reverse_iterator(const std::reverse_iterator<_Iter>&) [with _Iter = __gnu_cxx::__normal_iterator<const int*, std::vector<int, std::allocator<int> > >, _Iterator = __gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> > >]’:
frag.cpp:14:   instantiated from here
/usr/include/c++/4.4/bits/stl_iterator.h:134: error: no matching function for call to ‘__gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> > >::__normal_iterator(__gnu_cxx::__normal_iterator<const int*, std::vector<int, std::allocator<int> > >)’
/usr/include/c++/4.4/bits/stl_iterator.h:686: note: candidates are: __gnu_cxx::__normal_iterator<_Iterator, _Container>::__normal_iterator(const _Iterator&) [with _Iterator = int*, _Container = std::vector<int, std::allocator<int> >]
/usr/include/c++/4.4/bits/stl_iterator.h:683: note:                 __gnu_cxx::__normal_iterator<_Iterator, _Container>::__normal_iterator() [with _Iterator = int*, _Container = std::vector<int, std::allocator<int> >]
/usr/include/c++/4.4/bits/stl_iterator.h:669: note:                 __gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> > >::__normal_iterator(const __gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> > >&)

昨天有一个关于这个问题的问题,但我不认为这是一个问题,因为它不是一个模板.如果在本地以类似的方式声明向量,则非常高兴.(在Ubuntu 10.4上使用g ++).

谁知道我应该怎么做？

Answer 1

你需要使用const_reverse_iterator(print是一个const函数,以便a为const)和a.rbegin()和a.rend(),而不是begin()和end().