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：