Exer17_18.cpp

// Note: this program uses dictionary file ./data/wordsEn.txt.
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <algorithm>
#include <regex>
using std::cout;
using std::cerr;
using std::cin;
using std::endl;
using std::ifstream;
using std::string;
using std::vector;
using std::regex;
using std::smatch;
using std::sregex_iterator;
int main(int argc, char* argv[])
{
    vector<string> dict; // dictionary vector
    if(argc != 2) {
        cerr << "no dictionary is offered! Won't use any dictionary!" << endl;
    } else {
        ifstream is(argv[1]);
        string word;
        while(is >> word)
            dict.push_back(word);
    }
    string file;
    // find the characters ei that follow a character other than c
    string pattern("[^c]ei");
    // we want the whole word in which our pattern appears
    pattern = "[[:alpha:]]*" + pattern + "[[:alpha:]]*";
    regex r(pattern, regex::icase); // we'll ignore case in doing the match
    // it will repeatedly call regex_search to find all matches in filebuf
    while(getline(cin, file)) {
        for (sregex_iterator it(file.begin(), file.end(), r), end_it;
            it != end_it; ++it) {
            if (dict.empty() || !binary_search(dict.begin(), dict.end(), it->str())) {
                auto pos = it->prefix().length(); // size of prefix
                pos = (pos > 40) ? (pos - 40) : 0; // we want up to 40 characters
                cout << it->prefix().str().substr(pos) // last part of the prefix
                     << "\n\t\t>>> " << it->str() << " <<<\n" // matched word
                     << it->suffix().str().substr(0, 40) // first part of the suffix
                     << endl;
            }
        }
    }
    return 0;
}