這是在《C++ Primer》上第十章最后的一個小節。以前把這里漏掉了，剛才看了下，覺得這個程序很不錯，便于對vector, map, set的基本掌握。特地把這一個小程序記錄下來。
/*
*目的：一個簡單的文本查詢程序
*作用：程序將讀取用戶指定的任意文本文件，然后允許用戶從該文件中查找單詞。
*查詢的結果是該單詞出現的次數，并列出每次出現所在的行。
*如果某單詞在同一行中多次出現，程序將只顯示該行一次。
*行號按升序顯示，即第 7 行應該在第 9 行之前輸出，依此類推。
*/
/*思路：
*1.使用一個 vector<string> 類型的對象存儲整個輸入文件的副本。
* 輸入文件的每一行是該 vector 對象的一個元素。
* 因而，在希望輸出某一行時，只需以行號為下標獲取該行所在的元素即可。
*2.將每個單詞所在的行號存儲在一個 set 容器對象中。
* 使用 set 就可確保每行只有一個條目，而且行號將自動按升序排列。
*3.使用一個 map 容器將每個單詞與一個 set 容器對象關聯起來，
* 該 set 容器對象記錄此單詞所在的行號。
*/
TextQuery.H文件
#ifndef TEXTQUERY_H
#define TEXTQUERY_H
#include <string>
#include <vector>
#include <map>
#include <set>
#include <iostream>
#include <fstream>
#include <cctype>
#include <cstring>
class TextQuery {
// as before
public:
// typedef to make declarations easier
typedef std::string::size_type str_size;
typedef std::vector<std::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(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;
str_size size() const { return lines_of_text.size(); }
void display_map(); // debugging aid: print the map
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;
// characters that constitute whitespace
static std::string whitespace_chars;
// canonicalizes text: removes punctuation and makes everything lower case
static std::string cleanup_str(const std::string&);
};
#endif
TextQuery.CPP 文件
#include "TextQuery.h"
#include <sstream>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <iostream>
#include <fstream>
#include <cctype>
#include <cstring>
#include <stdexcept>
using std::istringstream;
using std::set;
using std::string;
using std::getline;
using std::map;
using std::vector;
using std::cerr;
using std::cout;
using std::cin;
using std::ifstream;
using std::endl;
using std::ispunct;
using std::tolower;
using std::strlen;
using std::out_of_range;
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");
}
// 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);
}
// \v: vertical tab; \f: formfeed; \r: carriage return are
// treated as whitespace characters along with space, tab and newline
string TextQuery::whitespace_chars(" \t\n\v\r\f");
// 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[cleanup_str(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(cleanup_str(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;
}
void TextQuery::display_map()
{
map< string, set<line_no> >::iterator iter = word_map.begin(),
iter_end = word_map.end();
// for each word in the map
for ( ; iter != iter_end; ++iter) {
cout << "word: " << iter->first << " {";
// fetch location vector as a const reference to avoid copying it
const set<line_no> &text_locs = iter->second;
set<line_no>::const_iterator loc_iter = text_locs.begin(),
loc_iter_end = text_locs.end();
// print all line numbers for this word
while (loc_iter != loc_iter_end)
{
cout << *loc_iter;
if (++loc_iter != loc_iter_end)
cout << ", ";
}
cout << "}\n"; // end list of output this word
}
cout << endl; // finished printing entire map
}
// lower-case to upper-case
string TextQuery::cleanup_str(const string &word)
{
string ret;
for (string::const_iterator it = word.begin(); it != word.end(); ++it) {
if (!ispunct(*it))
ret += tolower(*it);
}
return ret;
}
主函數
#include "TextQuery.h"
#include <string>
#include <vector>
#include <map>
#include <set>
#include <iostream>
#include <fstream>
#include <cctype>
#include <cstring>
#include <cstdlib>
using std::set;
using std::string;
using std::map;
using std::vector;
using std::cerr;
using std::cout;
using std::cin;
using std::ifstream;
using std::endl;
string make_plural(size_t, const string&, const string&);
ifstream& open_file(ifstream&, const string&);
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) {
cout << "\t(line "
// don't confound user with text lines starting at 0
<< (*it) + 1 << ") "
<< file.text_line(*it) << endl;
}
}
// program takes single argument specifying the file to query
int main()
{
// open the file from which user will query words
ifstream infile;
if (!open_file(infile, "Tanky_Woo.txt")) {
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;
}
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(); // close in case it was already open
in.clear(); // clear any existing errors
// if the open fails, the stream will be in an invalid state
in.open(file.c_str()); // open the file we were given
return in; // condition state is good if open succeeded
}
posted on 2010-11-11 20:16
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