Exer11_38_2.cpp

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <unordered_map>
#include <stdexcept>
using std::cout;
using std::endl;
using std::ifstream;
using std::istringstream;
using std::string;
using std::unordered_map;
using std::runtime_error;
unordered_map<string, string> buildMap(ifstream &map_file)
{
    unordered_map<string, string> trans_map;
    string key, value;
    while(map_file >> key && getline(map_file, value))
    {
        if(value.size() > 1)
            trans_map[key] = value.substr(1);
        else
            throw runtime_error("no rule for " + key + " at " + __func__);
    }
    return trans_map;
}
const string& transform(const string &s, const unordered_map<string, string> &m)
{
    auto map_it = m.find(s);
    if(map_it != m.cend())
        return map_it->second;
    else
        return s;
}
void word_transform(ifstream &map_file, ifstream &input)
{
    auto trans_map = buildMap(map_file);
    string text;
    while(getline(input, text))
    {
        istringstream stream(text);
        string word;
        bool firstword = true;
        while(stream >> word)
        {
            // process leading space
            if(firstword)
                firstword = false;
            else
                cout << " ";
            // process word
            cout << transform(word, trans_map);
        }
        cout << endl;
    }
}
int main(int argc, char *argv[])
{
    if(argc != 3)
        return -1;
    ifstream map_file(argv[1]), input_file(argv[2]);
    try
    {
        word_transform(map_file, input_file);
    }
    catch(runtime_error err)
    {
        cout << "Error: " << err.what() << endl;
    }
    return 0;
}