1 该程序将读取用户指定的任意文本文件，然后允许用户从该文件中查找单词。查询的结果是该单词出现的次数，并列出每次出现所在的行。如果某单词在同一行中多次出现，程序将只显示该行一次，行号按升序显示。
  2 
  3 以下是代码实现：
  4 
  5 #include <ctype.h>
  6 #include <iostream>
  7 #include <string>
  8 #include <map>
  9 #include <set>
 10 #include <vector>
 11 #include <sstream>
 12 #include <fstream>
 13 #include <algorithm>
 14 #include <iterator>
 15 using std::cout;
 16 using std::endl;
 17 using std::map;
 18 using std::set;
 19 using std::vector;
 20 using std::string;
 21 using std::ifstream;
 22 using std::ofstream;
 23 using std::istringstream;
 24 
 25 class Query
 26 {
 27     public:
 28         void readFile(const string filename);
 29         void query(const string & world);
 30 
 31     private:
 32         vector<string> _lines;
 33         map<string,set<int>> word2line;
 34         map<string,int> _wordFreq;
 35 };
 36 
 37 void Query::readFile(const string filename)
 38 {
 39     ifstream ifs(filename);
 40     if(!ifs.good())
 41     {
 42         cout << "Oops!" << endl;
 43         return;
 44     }
 45     string line;
 46     int setnumber = 0;
 47     while(getline(ifs,line))
 48     {
 49         _lines.push_back(line);
 50         ++setnumber;
 51         istringstream iss(line);
 52         string word;
 53         while(iss >> word)
 54         {
 55             map<string,int>::iterator it = _wordFreq.begin();
 56             while(it != _wordFreq.end())
 57             {    
 58                 if(word==it->first)
 59                 {
 60                     ++(it->second);
 61                     word2line[word].insert(setnumber);
 62                     break;
 63                 }
 64                 ++it;
 65             }
 66             if(it == _wordFreq.end())
 67             {
 68                 _wordFreq[word]=1;
 69                 word2line[word].insert(setnumber);
 70             }
 71         }   
 72     }
 73     ifs.close();
 74 }
 75 
 76 void Query::query(const string & word)
 77 {
 78     if(!_wordFreq[word]) 
 79     {
 80         cout << "word:" << word << " --> Not found!" << endl;
 81     }
 82     else
 83     {
 84         cout << word << " occurs " << _wordFreq[word] << " times." << endl;
 85         for(auto & elem : word2line[word])
 86         {
 87             cout << "   (line " << elem << ") " << _lines[elem-1] << endl;
 88         }
 89     }
 90 }
 91 
 92 int main(int argc,char *argv[])
 93 {
 94     if(argc!=3)
 95     {
 96         cout << "Oops!" << endl;
 97         return -1;
 98     }
 99     Query qur;
100     qur.readFile(argv[1]);
101     qur.query(argv[2]);
102 
103     return 0;
104 }