ex19_20.cpp

#include <iostream>
#include <vector>
#include <string>
#include <fstream>
#include <memory>
#include <map>
#include <set>
#include <sstream>
class TextQuery {
	public:
		class QueryResult;
		using line_no = std::vector<std::string>::size_type;
		TextQuery(std::ifstream&);
		TextQuery::QueryResult query(const std::string&) const;
	private:
		std::shared_ptr<std::vector<std::string> > file;
		std::map<std::string, std::shared_ptr<std::set<line_no> > > wm;	
};

class TextQuery::QueryResult{
	friend std::ostream& print(std::ostream&, const QueryResult&);
	public:
		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; //query word
		std::shared_ptr<std::set<line_no> > lines; //lines the word show
		std::shared_ptr<std::vector<std::string> > file; //files show the word;
};

TextQuery::TextQuery(std::ifstream &is) : file(new std::vector<std::string> ){
	std::string text;
	while (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 std::set<line_no>);	
			}
			lines->insert(n);
		}
	}
}

TextQuery::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 TextQuery::QueryResult(sought, nodata, file);		
	}
	else {
		return TextQuery::QueryResult(sought,loc->second,file);
	}
}

std::ostream &print (std::ostream & os, const TextQuery::QueryResult & qr)
{
	os << qr.sought << " occurls " << qr.lines->size() << " time(s)" << std::endl; 
	for (auto i : *qr.lines) {
		os << "\t(line " << i+1 << ") " << *(qr.file->begin() + i) << std::endl;	
	}
	return os;
}

int main(int argc, char *argv[])
{
	std::ifstream file;
	file.open("ex19_18.cpp");
	TextQuery si(file);
	auto res = si.query("std");
	print(std::cout, res);
	return 0;
}