c++ - 迭代器操作不起作用

Question

出于某种原因，在此函数中，它计算两个或多个相同值的“团 block ”:

#include <iostream>
#include <iterator> 
#include <set>

int countClumps(multiset<int> set)
{
    int clumps = 0;

    for (multiset<int>::const_iterator iter(set.begin()), end(set.end()); iter != end; ++iter)
    {
        if (iter == iter[1] && iter != iter[-1])
        {
            clumps += 1;
        }
    }
    return clumps;
}

我收到错误消息“没有运算符‘[]’匹配这些操作数”。为什么会这样？我认为像 iter[i] 和 *(iter + i) 这样的东西是标准操作？我确实尝试过 *(iter + 1) 但这给了我相同的操作数错误但带有 +。是否有我忘记包含的内容？

Answer 1

I get the error "no operator '[]' matches these operands". Why would this happen?

那是因为operator[] multiset<int>::const_iterator 不支持.

I thought stuff like iter[i] and *(iter + i) were standard operations?

你想错了。

I did try *(iter + 1) but that gave me the same operand error but with +. Was there something that I've forgotten to include?

operator+ multiset<int>::const_iterator 之间不支持和一个 int .因此，iter + 1不是有效的表达式。

您没有忘记添加任何内容。您正在尝试对象类型不支持的操作。

您将不得不重新考虑您的代码。

---

按照以下实现方式应该可以工作。

int countClumps(multiset<int> set)
{
   int clumps = 0;
   int previousNumber = 0;

   multiset<int>::const_iterator iter(set.begin());
   multiset<int>::const_iterator end(set.end());

   // Account for empty input.
   if ( iter != end )
   {
      previousNumber = *iter;

      for (++iter; iter != end; )
      {
         if ( previousNumber == *iter )
         {
            ++clumps;

            // Skip the rest of the clump
            for ( ++iter; iter != end && previousNumber == *iter ; ++iter );
         }
         else
         {
            ++iter;
         }

         if ( iter != end )
         {
            previousNumber = *iter;
         }

      }
   }
   return clumps;
}