C++ - 在文件中 查找 指定的词 出现的行号 (shared_ptr)

/* 
 * cppprimer.cpp 
 * 
 *  Created on: 2013.11.7 
 *      Author: Caroline 
 */  
  
#include <iostream>  
#include <fstream>  
#include <sstream>  
#include <string>  
#include <vector>  
#include <memory>  
  
#include <set>  
#include <map>  
  
using namespace std;  
  
class QueryResult;  
std::ostream& print(std::ostream& os, const QueryResult &qr);  
  
class TextQuery {  
public:  
    using line_no = std::vector<std::string>::size_type;  
    TextQuery(std::ifstream& );  
    QueryResult query(const std::string& ) const;  
private:  
    std::shared_ptr<std::vector<std::string> > file; //文件内容  
    std::map<std::string, std::shared_ptr<std::set<line_no> > > wm; //词和行号的集合  
};  
  
/*把每一行放入text, 存入file(vector), 组成word和行号(set)的映射*/  
TextQuery::TextQuery(std::ifstream &is) : file(new std::vector<std::string>)  
{  
    std::string text;  
    while (std::getline(is, text)) {  
        file->push_back(text);  
        int n = file->size() - 1;  
        std::istringstream line(text);  
        std::string word;  
        while (line >> word) {  
            auto& lines = wm[word];  
            if (!lines)  
                lines.reset(new set<line_no>);  
            lines->insert(n);  
        }  
    }  
}  
  
class QueryResult {  
friend std::ostream& print (std::ostream&, const QueryResult& );  
public:  
    using line_no = std::vector<std::string>::size_type;  
    QueryResult (std::string s,  
            std::shared_ptr<std::set<line_no>> p,  
            std::shared_ptr<std::vector<std::string>> f) :  
                sought(s), lines(p), file(f) {}  
private:  
    std::string sought; //查找字符串  
    std::shared_ptr<std::set<line_no>> lines; //行号集合  
    std::shared_ptr<std::vector<std::string>> file; //文件集合  
};  
  
/*找到指定sought的集合, 返回迭代器, 传入string和set*/  
QueryResult TextQuery::query(const std::string& sought) const {  
    static std::shared_ptr<std::set<line_no>> nodata(new std::set<line_no>);  
    auto loc = wm.find(sought);  
    if (loc == wm.end())  
        return QueryResult(sought, nodata, file); //没有找到, 不打印  
    else  
        return QueryResult(sought, loc->second, file); //按行号打印  
};  
  
std::string make_plural (std::size_t ctr, const std::string& word,  
        const std::string ending)  
{  
    return (ctr > 1) ? word + ending : word;  
}  
  
std::ostream& print(std::ostream& os, const QueryResult &qr){  
    os << qr.sought << " occurs " << qr.lines->size() << " "  
            << make_plural(qr.lines->size(), "time", "s") << std::endl;  
    for(auto num : *qr.lines)  
        os << "\t(line " << num+1 << ") " << *(qr.file->begin()+num) << std::endl;  
    return os;  
}  
  
void runQueries (std::ifstream &infile) {  
    TextQuery tq(infile);  
    while (true) {  
        std::cout << "enter word to look for, or q to quit: ";  
        std::string s;  
        if ( !(cin>>s) || s == "q" ) break;  
        print(std::cout, tq.query(s)) << std::endl;  
    }  
}  
  
int main (void) {  
  
    std::ifstream infile;  
    infile.open("file.txt");  
    runQueries(infile);  
    infile.close();  
  
    return 0;  
  
}