问题： c++ primer 习题11.18的答案

#include <string>
#include <iostream>
#include <list>
#include <vector>
#include <set>
#include <map>
#include <utility>
using namespace std;
int main()
{
cout << "first time:" << endl;
map<string,size_t> word_count{
  
  {"study",2},{"hard",4},{"very",123},{"beautiful",12}};
//下面这个map<string,size_t>::const_iterator类型却能够运行正确？到底是哪个
map<string,size_t>::const_iterator it = word_count.cbegin();
while(it != word_count.cend())
 {
cout << it->first << " occurs "
     << it->second << " times" << endl;
   ++ it;
 }



cout << "second times " << endl;
//答案说是类型是:pair<const string,size_t>::iterator，例如下面，但是运行确出错
pair<const string,size_t&g