C++ 容器 综合应用 文本查询程序

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

using namespace std;

class TextQuery
{
public:
// typedef to make declarations easier
typedef vector<string>::size_type line_no;
/* interface:
* read_file builds internal 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(ifstream &is) { store_file(is); build_map(); }
set<line_no> run_query(const string&) const;
string text_line(line_no) const;
private:
// utility functions used by read_file
void store_file(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
map< string, set<line_no> > word_map;
};

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

// finds 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'll 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 out_of_range("line number out of range");
}

string make_plural(size_t ctr,const string &word, const string &ending)
{
//make_plural(wc, "word ", "s ")当输入中文本中
//word数大于一是在word后加s，为words为word的复数！
return (ctr==1) ? word : word+ending;
}

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 occurrences
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)
{
// don't confound user with text lines starting at 0
cout << "\t(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)
{
// open the file from which user will query words
ifstream infile;
if (argc < 2 || !open_file(infile, argv[1]))
{
cerr << "No input file!" << endl;
return EXIT_FAILURE;
}
TextQuery tq;
tq.read_file(infile); // builds 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;
// stop if hit eof on input or a 'q'is entered
if (!cin || s == "q")
break;
// get the set of line numbers on which this word appears
set<TextQuery::line_no> locs = tq.run_query(s);
// print count and all occurrences, if any
print_results(locs, s, tq);
}
return 0;
}