c++ primer 第十章 容器的综合应用:文本查询程序

        功能:程序将读取用户指定的任意文本文件,然后允许用户从该文件中查找单词.查询的结果是该单词出现的次数,并列出每次出现所在的行.如果某单词在同一行中多次出现,程序将只显示该行一次.
行号按升序显示,即第7行应该在第9行之前输出,依次类推.

 程序需要支持如下任务:
(1) 它必须允许用户指明要处理的文件名字. 程序将存储该文件的内容,以便输出每个单词所在的原始行.
(2) 它必须将每一行分解为各个单词,并记录每个单词所在的所有行. 在输出行号时,应保证以升序输出,并且不重复.
(3) 对特定单词的查询将返回出现该单词的所有行的行号.
(4) 输出某单词所在的行文本时, 程序必须能根据给定的行号从输入文件中获取相应的行.
数据结构
(1)  使用一个vector类型的对象存储整个输入文件的副本, 输入文件的每一行是该ｖｅｃｔｏｒ对象的一个元素.
(2)  将每个单词所在的行号存储在一个ｓｅｔ容器对象中.使用ｓｅｔ就可确保每行只有一个条目,而且行号将自动按升序排列；
(3)  使用一个ｍａｐ容器将每个单词与一个ｓｅｔ容器对象关联起来,该ｓｅｔ容器对象记录此单词所在的行号.

代码:

/*************************************************************************
    > File Name: textquery.cpp
    > Author: wolf
    > Created Time: Thu 27 Jun 2013 03:12:07 PM CST
 ************************************************************************/

#include<iostream>
#include<fstream>
#include<sstream>
#include<vector>
#include<map>
#include<set>
#include<stdexcept>
#include<cstdlib>

using namespace std;

class TextQuery    {
public:
    //typedef to make declarations easier
    typedef std::vector<std::string>::size_type line_no;
    /*
     * read_file builds internel data structures for the given file
     * run_query finds the given word and returns set of lines on which it appears
     * text_line returns a requested line from the input file
     */
     void read_file(std::ifstream &is)
     { store_file(is); build_map();     }
     std::set<line_no> run_query(const std::string &) const;
     std::string text_line(line_no) const;

private:
     //utility functions used by read_file
     void store_file(std::ifstream&); //store input file
     void build_map(); //associated each word with a set of line numbers
     //remember the whole input file
     std::vector<std::string> lines_of_text;
     //map word to set of the lines on which it occurs
     std::map< std::string, std::set<line_no> > word_map;
};

// read input file: store each line as element in line_of_text
void TextQuery::store_file(ifstream &is)
{
    string textline;
    while(getline(is, textline))
        lines_of_text.push_back(textline);
}

// fine whitespace-separated words in the input vector
// and puts the word in word_map along with the line number
void TextQuery::build_map()
{
    //process each line from the input vector
    for(line_no line_num = 0; line_num != lines_of_text.size(); ++line_num)
    {
        //we will use line to read the text  a word at a time
        istringstream line(lines_of_text[line_num]);
        string word;
        while(line >> word)
            //add this 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
        //fetch and return set of line numbers for this word
        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 == 1) ? word: word +ending;
}

ifstream& open_file(ifstream &in, const string &file)
{
    in.close();
    in.clear();
    in.open(file.c_str());
    return in;
}


void print_results(const set<TextQuery::line_no> &locs, const string &sought, const TextQuery &file)
{
    //if the word was found, then print count and all occurences
    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;
    //print each line in which the word appeared
    line_nums::const_iterator it = locs.begin();
    for(; it != locs.end(); it++)
    {
        cout << "\t(line " << (*it) + 1 << ")" << file.text_line(*it) << endl;
    }
}


int main(int argc, char *argv[])
{
    ifstream infile;
    if(argc < 2 || !open_file(infile, argv[1]))
    {
        cerr << "No input file!" << endl;
        return EXIT_FAILURE;
    }
    TextQuery tq;
    tq.read_file(infile);
    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_results(locs, s, tq);
    }

    return 0;
}