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=0;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==1)?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<<"
"<<sought<<" occurs "
        <<size<<" "
        <<make_plural(size,"time","s")<<endl;
    line_nums::const_iterator it=locs.begin();
    for(;it!=locs.end();++it)
    {
        cout<<"	(line "
            <<(*it)+1<<") "
            <<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<2||!open_file(infile,argv[1]))
    {
        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 0;
}

运行结果：