std :: insert_iterator和iterator无效 [英] std::insert_iterator and iterator invalidation

问题描述

我试着写一个泛型， intersperse 函数。该函数应该将一个给定的元素穿插到一个元素序列中。

I tried writing a generic, in place, intersperse function. The function should intersperse a given element into a sequence of elements.

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

template<typename ForwardIterator, typename InserterFunc>
void intersperse(ForwardIterator begin, ForwardIterator end, InserterFunc ins, 
                 // we cannot use rvalue references here, 
                 // maybe taking by value and letting users feed in std::ref would be smarter
                 const ForwardIterator::value_type& elem) {
  if(begin == end) return;
  while(++begin != end) {
    // bugfix would be something like:
    // begin = (ins(begin) = elem); // insert_iterator is convertible to a normal iterator
    // or
    // begin = (ins(begin) = elem).iterator(); // get the iterator to the last inserted element

    // begin now points to the inserted element and we need to
    // increment the iterator once again, which is safe
    // ++begin;
    ins(begin) = elem;
  }
}

int main()
{
  typedef std::list<int> container;
  // as expected tumbles, falls over and goes up in flames with:
  // typedef std::vector<int> container;
  typedef container::iterator iterator;
  container v{1,2,3,4};

  intersperse(v.begin(), v.end(), 
              [&v](iterator it) { return std::inserter(v, it); },
              23);
  for(auto x : v)
    std::cout << x << std::endl;
  return 0;
}

此示例仅适用于不会使其
迭代器无效的容器插入。我应该简单地摆脱迭代器和
接受一个容器作为参数，或者我缺少一些关于
insert_iterator ，使这种使用可能？

The example works only for containers that do not invalidate their iterators on insertion. Should I simply get rid of the iterators and accept a container as the argument or am I missing something about insert_iterator that makes this kind of usage possible?

推荐答案

此示例仅适用于插入时不会使其迭代器无效的容器。 p>

The example works only for containers that do not invalidate their iterators on insertion.

正确。

并接受一个容器作为参数

Should I simply get rid of the iterators and accept a container as the argument

这将是一种可能性。另一种方法是不将算法放在原位（即输出到不同的容器/输出迭代器）。

That would be one possibility. Another would be not making the algorithm in-place (ie. output to a different container/output-iterator).

关于insert_iterator，使这种使用可能吗？

am I missing something about insert_iterator that makes this kind of usage possible?

否。 insert_iterator 用于重复插入容器的单个位置，例如。通过变换算法。

No. insert_iterator is meant for repeated inserts to a single place of a container eg. by a transform algorithm.

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