1 Our program will read a file specified by the user and then allow the user to 
2 search the file for words that might occur in it. The result of a query will be 
3 the number of times the word occurs and a list of lines on which 
4 it appears. If a word occurs more than once on the same line, 
5 our program should be smart enough to display that line only once. 
6 Lines should be displayed in ascending orderthat is, 
7 line 7 should be displayed before line 9, and so on.

#ifndef __TEXTQUERY_H__
#define __TEXTQUERY_H__

#include <iostream>
#include <istream>
#include <fstream>
#include <vector>
#include <map>
#include <set>
#include <utility>
#include <string>

typedef std::vector<std::string>::size_type line_no;

class TextQuery {
    public:
        // interface:
        void read_file(std::ifstream &is) {
            store_file(is);
            build_map();
        }
        std::set<line_no> run_query(const std::string &) const;
        std::string text_line(line_no) const;
    private:
        // utility functions used by read_file
        void store_file(std::ifstream&);
        void build_map(); // associate each word with a set of line numbers
        // remember the whole input file
        std::vector<std::string> lines_of_text;
        // map word to set of the lines on which it occurs
        std::map< std::string, std::set<line_no> > word_map;
};

#endif

// opens in binding it to the given file
ifstream& open_file(ifstream &in, const string &file)
{
    in.close();     // close in case it was already open
    in.clear();     // clear any existing errors
    
    // if the open fails, the stream will be in an invalid state
    in.open(file.c_str()); // open the file we were given
    
    return in; // condition state is good if open succeeded
}

#include "TextQuery.h"

define    EXIT_FAILURE    -1

using namespace std;

int main(int argc, char *argv[])
{
    // open the file from which user will quer words 
    ifstream infile;
    if(argc < 2 || !open_file(infile, argv[1])){
        cerr << "No input file!" << endl;
        return EXIT_FAILURE;
    }
    TextQuery tq;
    tq.read_file(infile);
    
    // prompt for a word to file and print result
    while(true){
        cout << "Enter word to look for(or Q/q to Quit): \n" ;
        string str;
        cin >> str;
        // stop if hit eof on input or a 'Q' is entered 
        if(!cin || str == "Q" || str == "q")
            break;
        // get tje set of line numbers on which this word appears
        set<line_no> locs = tq.run_query(str);
        // print count an all occurrences, if any
        print_results(locs, str, tq);
    }
    
    return 0;
}

// return plural version of word if ctr isn't 1
string make_plural(size_t ctr, const string &word,
                            const string &ending)
{
    return (ctr == 1) ? word : word + ending;
}

void print_results(const set<line_no>& locs, 
                    const string& sought, const TextQuery& file)
{
    // if the word was found, then print count and all occurrences
    typedef set<line_no> line_nums;
    line_nums::size_type size = locs.size();
    cout << "\n" << sought << " occurs " << size << " "
         << make_plural(size, "time", "s") << endl;
         
     // print each line in which the word appeared
     line_nums::const_iterator it = locs.begin();
     for(; it != locs.end(); ++it){
         // don't confound user with text lines starting at 0
         cout << "\t(line" << (*it) +1 << ")" 
              << file.text_line(*it) << endl;
     }
}

#include "TextQuery.h"
#include <stdexcept>
#include <sstream>

using namespace std;

set<line_no> TextQuery::run_query(const string &query_word) const
{
    // must use find and not subscript he map directly
    // to avoid adding words to word_map
    map< string, set<line_no> >::const_iterator
                        loc = word_map.find(query_word);
    if(loc == word_map.end()){
        // not found, return empty set
        return set<line_no>(); 
    }
    else{
        // fectch and return set of line numbers for this word
        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");
}

// utility functions used by read_file
void TextQuery::store_file(ifstream &is)
{
    string textline;
    while (getline(is, textline))
        lines_of_text.push_back(textline);
}
        
// associate each word with a set of line numbers
void TextQuery::build_map()
{
    // process each line from the input vector
    for (line_no line_num = 0; line_num != lines_of_text.size(); ++line_num) {
        // we'll use line to read the text a word at a time
        istringstream line(lines_of_text[line_num]);
        string word;
        while (line >> word){
            // add this line number to the set;
            // subscript will add word to the map if it's not already there
            word_map[word].insert(line_num);
        }
    } 
}