C++ Primer第四版 15.9 再谈文本查询 程序实现

编程过程中发现书本中的示例程序并不完全，某些地方存在错误，现已改正并添加少许注释..

  1 #include<iostream>  
  2 #include<fstream>
 #include<sstream>
 #include<vector>
 #include<map>
 #include<set>
 #include<algorithm>
 #include<stdexcept>
 using namespace std;

 class TextQuery{
 public:
     typedef vector<string>::size_type line_no;
     void read_file(ifstream &is){
         store_file(is);     //读取并保存输入文件
         build_map();     //创建关联单词与行号的容器
     }
     set<line_no> run_query(const string&) const;    //根据输入的字符串，在map中查找，返回一个set集合，里面包含了该字符串在文件的所有行号
     line_no size() const {return lines_of_text.size();}
     string text_line(line_no) const;     //以行号为输入参数，返回该行的字符串
 private:
     void store_file(ifstream&);
     void build_map();
     vector<string> lines_of_text;    //容器lines_of_text保存文本的副本
     map<string,set<line_no> > word_map;    //first存的是单词，second存的是set集合，里面是单词所在的所有行号
 };

 void TextQuery::store_file(ifstream &is)    //将文本文件读入内存保存在lines_of_text容器中
 {
     string textline;
     while(getline(is,textline))     //逐行存入vector
     lines_of_text.push_back(textline);
 }

 void::TextQuery::build_map()
 {
     for(line_no line_num = ; line_num != lines_of_text.size(); ++line_num)
     {
         istringstream line(lines_of_text[line_num]);    //将vector中的文件内容逐行提取出来
         string word;
         while(line >> word)     //将每行字符串分解成单词，插入到map中，键是单词，值是行号
         word_map[word].insert(line_num);     //*********word_map[word]返回的是右值，是一个set对象，insert()函数是set的函数********
     }
 }

 set<TextQuery::line_no> TextQuery::run_query(const string &query_word) const
 {
     map<string,set<line_no> >::const_iterator loc = word_map.find(query_word);
     if(loc == word_map.end())
         return set<line_no>();
     else
         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");
 }

 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();    //set集合的大小即是该单词出现的次数
     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;    //原行号从0开始，+1进行修正
 }

 class Query_base{
     friend class Query; //接口只提供给Query使用，用户和派生类只能通过Query句柄使用Query_base类
 protected:
     typedef TextQuery::line_no line_no;
     virtual ~Query_base(){}
 private:
     //eval returns the |set| of lines that this Query matches
     virtual std::set<line_no> eval(const TextQuery&) const = ;
     //display prints the query
     virtual std::ostream& display(std::ostream& = std::cout) const = ;
 };

 class WordQuery: public Query_base{
     friend class Query;
     WordQuery(const std::string &s): query_word(s) {}
     std::set<line_no> eval(const TextQuery &t) const {return t.run_query(query_word);}
     std::ostream& display(std::ostream &os) const {return os<<query_word;}
     std::string query_word;
 };

 class Query{
     friend Query operator~(const Query&);
     friend Query operator|(const Query&, const Query&);
     friend Query operator&(const Query&, const Query&);

 public:
     Query(const std::string& word): q(new WordQuery(word)), use(new std::size_t()) { }
     Query(const Query &c): q(c.q), use(c.use) {++*use;}
     ~Query() {decr_use();}

     Query& operator=(const Query&);
     std::set<TextQuery::line_no> eval(const TextQuery &t) const {return q->eval(t);}
     std::ostream &display(std::ostream &os) const {return q->display(os);}

 private:
     Query(Query_base * query): q(query), use(new std::size_t()) {} //我们不希望普通用户代码定义Query_base对象。因为是private权限，操作符必须是友元
     Query_base * q;
     std::size_t *use;
     void decr_use()
     {
         if(--*use == )
         {
             delete q;
             delete use;
         }
     }
 };

 inline std::ostream& operator<<(std::ostream &os, const Query &q)
 {
     return q.display(os);
 }

 class NotQuery: public Query_base{
     friend Query operator~(const Query&);
     NotQuery(Query q): query(q){}
     std::set<line_no> eval(const TextQuery &) const;
     std::ostream& display(std::ostream &os) const {return os<<"~("<<query<<")";}
     const Query query;              //why const?
 };

 class BinaryQuery: public Query_base{   //未实现eval函数，因此是一个抽象类
 protected:
     BinaryQuery(Query left, Query right, std::string op): lhs(left), rhs(right), oper(op) {}
     std::ostream& display(std::ostream &os) const {return os<<"("<<lhs<<" "<<oper<<" "<<rhs<<")";}
     const Query lhs, rhs;
     const std::string oper;
 };

 class AndQuery: public BinaryQuery{
     friend Query operator&(const Query&, const Query &);
     AndQuery(Query left, Query right): BinaryQuery(left, right, "&") {}
     std::set<line_no> eval(const TextQuery&) const;
 };

 class OrQuery: public BinaryQuery{
     friend Query operator|(const Query&, const Query&);
     OrQuery(Query left, Query right): BinaryQuery(left, right, "|") {}
     std::set<line_no> eval(const TextQuery&) const;
 };

 set<TextQuery::line_no> OrQuery::eval(const TextQuery& file)const
 {
     set<line_no> right = rhs.eval(file),
              ret_lines = lhs.eval(file);
     ret_lines.insert(right.begin(), right.end());
     return ret_lines;
 }

 set<TextQuery::line_no> AndQuery::eval(const TextQuery& file) const
 {
     set<line_no> left = lhs.eval(file),
                 right = rhs.eval(file);
     set<line_no> ret_lines;
     set_intersection(left.begin(), left.end(), right.begin(), right.end(), inserter(ret_lines, ret_lines.begin())); //调用STL库函数进行容器的交集操作
     return ret_lines;
 }

 set<TextQuery::line_no> NotQuery::eval(const TextQuery& file) const     //const引用的对象，只能访问对象的const成员，所以size函数必须是const类型的
 {
     set<TextQuery::line_no> has_val = query.eval(file);
     set<line_no> ret_lines;
     for(TextQuery::line_no n = ; n != file.size(); ++n)
         if(has_val.find(n) == has_val.end())
             ret_lines.insert(n);
     return ret_lines;
 }

 inline Query operator~(const Query &oper)
 {
     return new NotQuery(oper);              //等价于Query_base * tmp = new NotQuery(oper); return Query(tmp);
 }

 inline Query operator|(const Query &lhs, const Query &rhs)
 {
     return new OrQuery(lhs,rhs);
 }

 inline Query operator&(const Query &lhs, const Query &rhs)
 {
     return new AndQuery(rhs,lhs);
 }

 int main()
 {
     ifstream infile;
     infile.open("C:\\1.txt");
     if(!infile)
     {
         std::cout<<"Cannot open file"<<std::endl;
         exit();
     }
     TextQuery tq;
     tq.read_file(infile);

         /* 该处填写要查找的内容逻辑表达式 */
         //set<TextQuery::line_no> locs = tq.run_query(s);
         //Query q = ~(Query("today") & Query("API"));
         Query q = Query("today is") & Query("and");
         set<TextQuery::line_no> locs = q.eval(tq);
         string s = "";
         print_results(locs,s,tq);
  return ;
 }

当然要想实现作者开头所展示的实时查询功能，还要下不少功夫，有能力的童鞋自己实现字符串的解析吧-_-