文本查询程序（c++）set,vector,map容器实现

#include<iostream>
#include<fstream>
#include<sstream>
#include<string>
#include<vector>
#include<map>
#include<set>
using namespace std;

class TextQuery{
public:
 typedef vector<string>::size_type line_no;
 void read_file(ifstream &is)
 {
  store_file(is);
  build_map();
 }

 set<line_no>  run_query(const string&) const;
 string  text_line(line_no) const;
private:
 void store_file(ifstream&);
 void build_map();
 vector<string>lines_of_text;
 map<string,set<line_no> >word_map;
};

string make_plural(size_t ctr,const string &word,const string &ending)
{
 return (ctr==1)?word:word+ending;
}

void print_results(const set<TextQuery::line_no>& locs,const string& sought,const TextQuery &file)
{
 typedef set<TextQuery::line_no>line_nums;
 line_nums::size_type size=locs.size();
 cout<<"\n"<<sought<<" occurs "<<size<<" "
  <<make_plural(size,"time","s")<<endl;
 
  line_nums::const_iterator it=locs.begin();
 for(;it!=locs.end();++it){
  cout<<"\t(line"
   <<*(it)+1<<")"
   <<file.text_line(*it)<<endl;
 }
}

void TextQuery::store_file(ifstream &is)
{
 string textline;
 while(getline(is,textline))
  lines_of_text.push_back(textline);
}

void TextQuery::build_map()
{
 for(line_no line_num=0;line_num!=lines_of_text.size();++line_num)
 {
  istringstream line(lines_of_text[line_num]);
  string word;
  while(line>>word)
   word_map[word].insert(line_num);
 }
}

set<TextQuery::line_no> TextQuery::run_query(const string &query_word)const
{
 map<string,set<line_no> >::const_iterator loc=word_map.find(query_word);
 if(loc==word_map.end())
  return set<line_no>();
 else
  return loc->second;
}

string TextQuery::text_line(line_no line)const
{
 if(line<lines_of_text.size())
  return lines_of_text[line];

 else
  cout<<"line too big!"<<endl;
}

ifstream& open_file(ifstream &in,const string &file)
{
 in.close();
 in.clear();
 in.open(file.c_str());
 return in;
}

   
int main(int argc,char **argv)
{
 ifstream infile;
 if(!open_file(infile,"f:\\file.txt"))
 {
  cout<<"no input file!"<<endl;
 }
 TextQuery tq;
 tq.read_file(infile);
 while(true)
 {
  cout<<"enter word to look for,or q to quit:";
  string s;
  cin>>s;
  if(!cin||s=="q")break;
  set<TextQuery::line_no>locs=tq.run_query(s);
  print_results(locs,s,tq);
 }
 return 0;
}