I/O Example: wc

Let’s write our own version of wc. Here’s a text file: lorem-ipsum.txt.

Let’s write a C++ code the counts the number of lines, words, and characters from the input file.

We don’t know how to take a command line argument (yet), so let’s just hardcode the file name into the program for now.

Listing 81 wc_example.cpp

#include <iostream>
#include <fstream>
#include <string>

int main() {

    // open the file

    std::ifstream input_file("lorem-ipsum.txt");

    if (! input_file.is_open()) {
        std::cout << "Error: invalid file" << std::endl;
        return 1;
    }

    // loop over line by line
    std::string line;

    unsigned int line_count{0};
    unsigned int char_count{0};
    unsigned int word_count{0};

    bool was_space = false;

    while (std::getline(input_file, line)) {

        // by design, getline drops the newline, so add it back here
        // so we can accurately capture line breaks and get the words
        // right
        line += "\n";

        for (auto c : line) {
            bool test = (c == ' ' || c == '\n');
            if (test) {
                // the current character is a space or newline

                // if the previous character was a space or newline
                // too, then just skip, otherwise, increment the word
                // counter and set was_space
                if (! was_space) {
                    word_count++;
                    was_space = true;
                }
            } else {
                was_space = false;
            }

            char_count++;
        }

        line_count++;

    }

    std::cout << "number of lines = " << line_count << std::endl;
    std::cout << "number of words = " << word_count << std::endl;
    std::cout << "number of characters = "
              << char_count << std::endl;

}

The trickiest part of this is counting words. There could be multiple spaces or newlines separating words. We count a word only when we encounter a space or newline for the first time.