Exer17_17.cpp

#include <iostream>
#include <string>
#include <regex>
using std::cout;
using std::cin;
using std::endl;
using std::string;
using std::regex;
using std::smatch;
using std::sregex_iterator;
int main()
{
    string file("receipt freind theif receive");
    // 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
    for (sregex_iterator it(file.begin(), file.end(), r), end_it;
        it != end_it; ++it) {
        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;
}