c++ - std::map::lower_bound 正在为大于 2000 的映射键生成核心转储

Question

对于下面的示例程序，lower_bound 正在生成核心转储。知道哪里可能出错吗？

另外，谁能解释下 lower_bound 和 upper_bound 算法在 C++ 中是如何工作的？

#include <iostream>
#include <map>

int main ()
{
  std::map<int,int> mymap;
  std::map<int,int>::iterator itlow,itup;

  mymap[100]=10;
  mymap[1000]=20;
  mymap[2000]=40;
  mymap[3000]=60;
  mymap[4000]=80;
  mymap[5000]=100;

  itlow=mymap.lower_bound (2001);
  itup=mymap.upper_bound (1500);

  std::cout<<(itlow->first)<<std::endl;
  std::cout<<(itup->first)<<std::endl;
  mymap.erase(itlow,itup);        // erases [itlow,itup)

  // print content:
  for (std::map<int,int>::iterator it=mymap.begin(); it!=mymap.end(); ++it)
    std::cout << it->first << " => " << it->second << '\n';

  return 0;
}

Answer 1

你有倒退的删除:

mymap.erase(itup, itlow);        // erases [itlow,itup)

您只能从较小的迭代器删除到第一个参数之后的迭代器。在这种情况下，您的迭代器指向值:

lower: 3000
upper: 2000
and itup < itlow

来自 lower_bound和 upper_bound

lower_bound 返回:

Returns an iterator pointing to the first element in the range [first,last) which does not compare less than val.

upper_bound 返回:

Returns an iterator pointing to the first element in the range [first,last) which compares greater than val.