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 file
	void read_file(std::ifstream &is){
		store_file(is);
			build_map();
	}
	//query the file return the times every word appears
	std::set<line_no> run_query(const std::string&) const;

	//return the line-number of the word
	std::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 appears
std::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 word
std::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 appears
		std::set<TextQuery::line_no> locs = tq.run_query(s);
		print_results(locs, s, tq);

	}
	return 0;
}