C++primer中的TextQuery（读取文本）

本题目对应于 C++primer（第四版）中 第十章的文本查询类（TextQuery）

用到的知识有：

顺序容器 vector

关联容器 set，map

标准输入输出流，文件流，字符串流

//写一个文件 从文件中读单词 输出单词的次数和所在的行数//...#include <iostream>#include <fstream>#include <sstream>#include <string>#include <set>#include <vector>#include <map>class TextQuery{public:typedef std::vector<std::string>::size_type line_no;//read the filevoid read_file(std::ifstream &is){store_file(is); build_map();   }//query the file return the times every word appearsstd::set<line_no> run_query(const std::string&) const;//return the line-number of the wordstd::string text_line(line_no) const;private:void store_file(std::ifstream &is);void build_map();std::vector<std::string> lines_of_text;std::map<std::string, std::set<line_no>> word_map;};void TextQuery::store_file(std::ifstream &is){std::string textline;while(std::getline(is, textline)){lines_of_text.push_back(textline);}}void TextQuery::build_map(){for(line_no line_num = 0; line_num != lines_of_text.size(); ++line_num){std::istringstream line(lines_of_text[line_num]);std::string word;while(line >> word){word_map[word].insert(line_num);}}}//read to get times of every word appearsstd::set<TextQuery::line_no> TextQuery::run_query(const std::string& query_word) const{std::map<std::string, std::set<line_no>>::const_iterator loc = word_map.find(query_word);if(loc == word_map.end()){return std::set<line_no>();}else{return loc->second;}}//read to get the line-number of the wordstd::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");}};std::string make_plural(size_t ctr, const std::string& word, const std::string& ending){return (ctr == 1) ? word : word + ending;}void print_results(const std::set<TextQuery::line_no>& locs, const std::string& sought, const TextQuery& file){typedef std::set<TextQuery::line_no> line_nums;line_nums::size_type size = locs.size();std::cout<< "\n" << sought << "occurs " << size << " " << make_plural(size, "time", "s") << std::endl;line_nums::const_iterator it = locs.begin();for(; it != locs.end(); ++it){std::cout << "\t(line" << (*it) + 1 << ")" <<file.text_line(*it) << std::endl;}}int main(){std::ifstream infile("F:\\input.txt");TextQuery tq;tq.read_file(infile);while(true){std::cout << "enter word to look for, or q to quit: ";std::string s;std::cin >> s;if(!std::cin || s == "q") break;// get the set of line numbers on which this word appearsstd::set<TextQuery::line_no> locs = tq.run_query(s);print_results(locs, s, tq);}return 0;}