文本查询程序.cpp

此程序为文本查询程序

#include <iostream>
#include <fstream>
#include <string>
#include <map>
#include <set>
#include <vector>
#include <sstream>
#include <stdexcept>//异常处理的部分 

class TextQuery {
     public:
         // typedef to make declarations easier
         typedef std::vector<std::string>::size_type line_no;
         /* interface:
          * read_file builds internal data structures for the given file
          * run_query finds the given word and returns set of lines on which it appears
          * text_line returns a requested line from the input file
          */
         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&); // store input file
         void build_map(); // associated 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;
     };

using namespace std;
     // read input file: store each line as element in lines_of_text
     void TextQuery::store_file(ifstream &is)
     {
         string textline;
         while (getline(is, textline))
            lines_of_text.push_back(textline);
     }

 // finds whitespace-separated words in the input vector
      // and puts the word in word_map along with the line number
      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);
          }
     }

set<TextQuery::line_no>
     TextQuery::run_query(const string &query_word) const
     {
         //Note: must use find and not subscript the 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())
         return set<line_no>(); // not found, return empty set
     else
         // fetch 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");
   }
   
      // 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
    }

     // 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<TextQuery::line_no>& locs,
                         const string& sought, const TextQuery &file)
      {
          // if the word was found, then print count and all occurrences
          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;

          // print each line in which the word appeared
          line_nums::const_iterator it = locs.begin();
          for ( ; it != locs.end(); ++it) {
              cout << "\t(line "
                   // don't confound user with text lines starting at 0
                   << (*it) + 1 << ") "
                   << file.text_line(*it) << endl;
          }
     }


int main(int argc, char *argv[])
{
 	         // open the file from which user will query 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); // builds query map
         // iterate with the user: prompt for a word to find and print results
         // loop indefinitely; the loop exit is inside the while
         while (true) {
             cout << "enter word to look for, or q to quit: ";
             string s;
             cin >> s;
             // stop if hit eof on input or a 'q'is entered
             if (!cin || s == "q") break;
             // get the set of line numbers on which this word appears
             set<TextQuery::line_no> locs = tq.run_query(s);
             // print count and all occurrences, if any
             print_results(locs, s, tq);
          }
        // return 0;



  system("pause");
  return 0;
}