WordCount.cpp

#include <iostream>
#include <fstream>
#include <cstdlib>
#include <string>
#include <cstring>
#include <cctype>
#include <algorithm>
#include <unordered_map>
#include <set>

void printUsage(char*);
int countWords(std::string);
void getFrequency(std::string);

int main(int argc, char* argv[])
{
    if (argc < 2 || argc > 3) //Arguments can only be either <filename> or -f <filename>
    {
        printUsage(argv[0]);
        return EXIT_FAILURE;
    }

    if (std::string(argv[1]) == "-f")
    {
        if (argc != 3) //Arguments should only be -f and <filename> in this case
        {
            printUsage(argv[0]);
            return EXIT_FAILURE;
        }

        std::string filename(argv[2]);
        getFrequency(filename);
    }
    else
    {
        if (argc != 2) //Argument should be only <filename> in this case
        {
            printUsage(argv[0]);
            return EXIT_FAILURE;
        }

        std::string filename(argv[1]);
        int count = countWords(filename);
        std::cout << "The total number of words is: " << count;
    }

    return EXIT_SUCCESS;
}

void printUsage(char* path)
{
    std::cout << "Usage:\n";
    std::cout << "\t" << path << " <path to file>\n"
        << "\t"
        << "Output total number of words in file\n\n";
    std::cout << "\t" << path << " -f <path to file>\n"
        << "\t"
        << "Output frequency of all words in the file in ascending order, sorted lexicographically\n\n";
}

//Count total number of words in a file (word means a contigous group of non space characters)
int countWords(std::string filename)
{
    std::ifstream textFile(filename); //open file
    if (textFile)
    {
        int count = 0;
        std::string tmp;
        while (textFile >> tmp)
            ++count;

        return count;
    }
    else //if file open failed
    {
        char errmsg[256];
#ifdef _WIN32 //strerror_s for windows
        strerror_s(errmsg, sizeof(errmsg), errno);
#else //strerror_r for POSIX
        strerror_r(errno, errmsg, sizeof(errmsg));
#endif
        std::cerr << "The file could not be opened\n";
        std::cerr << "Error: " << errmsg << "\n";
        exit(EXIT_FAILURE);
    }
}

//print list of words with their frequency (case insensitive)
void getFrequency(std::string filename)
{
    std::ifstream textFile(filename); //open file
    if (textFile)
    {
        std::unordered_map<std::string, int> dict; //store words with their frequencies in an unordered map
        std::string word;
        while (textFile >> word)
        {
            std::transform(word.begin(), word.end(), word.begin(), ::tolower); //case insensitive: convert everything to lowercase
            if (dict.find(word) == dict.end())
                dict[word] = 1;
            else
                ++dict[word];
        }

        //save unordered map data into a set, which will sort it first by frequency and then by lexicographic order
        std::set<std::pair<int, std::string>> wordSet;
        for (auto x : dict)
            wordSet.insert(std::make_pair(x.second, x.first)); //frequency of the word first followed by the word itself

        //print
        for (auto x : wordSet)
            std::cout << x.first << " " << x.second << "\n";
        std::cout << std::endl;
    }
    else //if file opening failed
    {
        char errmsg[256];
#ifdef _WIN32 //use strerror_s for windows
        strerror_s(errmsg, sizeof(errmsg), errno);
#else
        strerror_r(errno, errmsg, sizeof(errmsg)); //and strerror_r for POSIX
#endif
        std::cerr << "The file could not be opened\n";
        std::cerr << "Error: " << errmsg << "\n";
        exit(EXIT_FAILURE);
    }
}