简单的文本查询工具

#include <iostream>
#include <fstream>
#include <string>
#include <set>
#include <map>
#include <vector>
#include<sstream>

using namespace std;

class TextQuery{
public:
    typedef std::vector<std::string>::size_type line_no;
    void read_file(std::ifstream & is)
    { store_file(is);build_map();}
    std::set<line_no> run_query(const string & ) const;
    std::string text_line(line_no) const;
private:
    void store_file(std::ifstream &);
    void build_map();
    std::vector<std::string> lines_of_text;
    std::map< string, std::set<line_no> > word_map;
};

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

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];
    throw std::out_of_range("line number out of range");
}
int main(int argc,char ** argv)
{
    ifstream infile;
    if (argc < 2 || !open_file(infile,argv[1]))
    {
        cerr<<"No input file!" <<endl;
        return EXIT_FAILURE;
    }
    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;
}