如何在c ++中从stdin读取字符串向量

Question

从“Accelerated C ++”一书中可以看出：

  

Ex 4-5-＆gt;编写一个从输入流中读取单词并将其存储在向量中的函数。使用该函数既可以编写计算输入中字数的程序，也可以计算每个单词出现的次数。

这是我试图运行的代码：

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using std::cin;       using std::cout;
using std::vector;    using std::sort;
using std::endl;      using std::string;
using std::istream;

istream& read_words(istream& in, vector<string>& words) {
  if (in) {
    words.clear();
    string word;

    while (in >> word)
      words.push_back(word);

    in.clear();
  }

  return in;
}

int main() {
  vector<string> words;

  read_words(cin, words);

  cout << "Num of words: " << words.size() << endl;

  sort(words.begin(), words.end());

  string prev_word = "";
  int count = 0;

  for (vector<string>::size_type i = 0; i < words.size(); ++i) {
    if (words[i] != prev_word) {
      if (prev_word != "")
         cout << prev_word << " appeared " << count << " times" << endl;

      prev_word = words[i];
      count = 1;
    }
    else
      ++count;
  }

  cout << prev_word << " appeared " << count << " times" << endl;

  return 0;
}

现在，当我尝试运行代码时，它会卡在输入端并继续读取 直到我使用 Ctrl + C 中止程序。我的代码出了什么问题？