C++关联容器综合应用：TextQuery小程序

本文介绍C++关联容器综合应用：TextQuery小程序（源自C++ Primer）。

关于关联容器的概念及介绍，请参考园子里这篇博文：http://www.cnblogs.com/cy568searchx/archive/2012/10/08/2715306.html

 #include<iostream>
 #include<fstream>
 #include<sstream>
 #include<string>
 #include<map>
 #include<vector>
 #include<set>
 using namespace std;
 //文本查询程序
 class TextQuery
 {
 public:
     typedef vector<string>::size_type line_no;

     void read_file(ifstream &is)
     {
         store_file(is);
         build_map();
     }
     set<line_no> run_query(const string&) const;
     string text_line(line_no) const;
 private:
     void store_file(ifstream&);
     void build_map();
     vector<string> lines_of_text;
     map<string,set<line_no> > word_map;
 };
 void TextQuery::store_file(ifstream &is)
 {
     string textline;
     while(getline(is,textline))
         lines_of_text.push_back(textline);
 }
 void TextQuery::build_map()
 {
     //process each line
     for(line_no line_num=;line_num!=lines_of_text.size();++line_num)
     {
         istringstream line(lines_of_text[line_num]);
         string word;
         while(line>>word)
             //add thie 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
         return loc->second;
 }
 string TextQuery::text_line(line_no line) const
 {
     if(line<lines_of_text.size())
         return lines_of_text[line];
     throw out_of_range("line number out of range");
 }
 string make_plural(size_t ctr,const string &word,const string &ending)
 {
     return (ctr==)?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)+<<") "
             <<file.text_line(*it)<<endl;
     }
 }
 ifstream& open_file(ifstream &in,const string &file)
 {
     in.close();
     in.clear();

     in.open(file.c_str());
     return in;
 }
 //program takes single argument specifying the file to query
 int main(int argc,char **argv)
 {
     ifstream infile;
     if(argc<||!open_file(infile,argv[]))
     {
         cerr<<"No input file!"<<endl;
         return EXIT_FAILURE;
     }
     TextQuery tq;
     tq.read_file(infile);//build 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;
         if(!cin||s=="q") break;
         set<TextQuery::line_no> locs=tq.run_query(s);
         //print count and all occurrences, if any
         print_results(locs,s,tq);
     }
     return ;
 }

运行结果：