inverted_index.cpp

#include <iostream>
#include <iterator>
#include <fstream>
#include <map>
#include <vector>
#include <string>

using index_type = std::map<std::string, std::vector<std::string>>;

bool AppendToIndex(index_type& index, std::string filename) {
    std::ifstream file(filename);

    if (!file.is_open())
        return false;

    while (!file.eof()) {
        std::string word;
        file >> word;

        auto inserted = index.insert({word, {filename}});

        if (!inserted.second)
            inserted.first->second.push_back(filename);
    }

    return true;
}

int main() {
    index_type index{};

    for (auto s : {"file1.txt", "file2.txt", "file3.txt"}) {
        if (!AppendToIndex(index, s))
            std::cout << "Warning: could not open " << s << "!\n";
    }

    std::string line;

    while (true) {
        std::cout << "Enter a word to search or hit return to exit: ";

        if (!std::getline(std::cin, line) || line.empty())
            break;

        auto pos = index.find(line);

        if (pos == index.end())
            std::cout << "Word was found in none of the files!\n";
        else {
            std::cout << "Word was found in: {";
            std::copy(pos->second.begin(), pos->second.end(),
                std::ostream_iterator<std::string>(std::cout, ", "));
            std::cout << "\b\b}\n";
        }
    }
}