推进std :: copy中的列表迭代器时出错

Question

#include <iostream>
#include <list>
#include <algorithm>
#include <iterator>
using std::list;
using std::endl;
using std::cout;
using std::iterator;
int main()
{
    list<int> list_int{ 0,1,2,3,4,5,6,7,8,9 };
    list<int> list_int2;

    copy(list_int.crbegin()+3 , list_int.crbegin()+8,back_inserter(list_int2));
    for (auto &ele : list_int2)
        cout << ele << endl;

    return 0;
}

what is the wrong?I am so confused.I think the wrong is about the copy function.

error：

Answer 1

You cannot advance a list iterator (bidirectional non-random) by incrementing it with more than one. In other words, only operator++ and operator-- are defined for bi-directional iterators. Use std::next instead,

copy(std::next(list_int.crbegin(), 3), 
     std::next(list_int.crbegin(), 8),
     back_inserter(list_int2));

std::next will tag-dispatch to the correct internal iterator function which in effect will increment the iterator one by one repeatedly.

Answer 2

list_int and list_int2 are of type std::list . Iterators of std::list do not support random access. Therefore you cannot advance them by adding an integer like list_int.crbegin() + 3 .

You can make a copy of the list iterators and use std::advance to advance them. See docs