main.cpp

// Text file input and output
// Chris Bass
// Updated October 2019

// note: requires C++17 for the filesystem library
// in VS2019 project > C/C++ > properties > language > C++ language standard > C++17 or above
// in CLion > Edit Run Configurations... > Working Directory > Insert Macros... > $ProjectFileDir$

#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>
#include <filesystem>

using namespace std;

int main(int argc, char *argv[]) {
    cout << "being executed from:" << endl;
    cout << argv[0] << endl;

    std::filesystem::path cwd = std::filesystem::current_path() / "filename.txt"; // C++17
    cout << "but the input.txt and output.txt files should be be in the following directory:" << endl;
    cout << cwd.string() << endl << endl;

    // writing to a text file using an output file stream object
    {
        cout << "--writing to output.txt started--" << endl;

        ofstream outputFileStream;

        outputFileStream.open("output.txt");
        outputFileStream << "Hello text file!" << endl;
        outputFileStream << "This will be inside output.txt" << endl;
        outputFileStream.close();

        cout << "--writing to output.txt finished--" << endl << endl;
    }

    // reading from a text file using an input file stream object
    {
        cout << "--reading from input.txt started--" << endl;

        ifstream inputFileStream;

        inputFileStream.open("input.txt");

        if (inputFileStream.good()) {
            cout << "Input file is good start processing" << endl;

            char inputChar = inputFileStream.get();

            while (!inputFileStream.fail()) {
                cout << inputChar;
                inputChar = inputFileStream.get();
            }

            cout << endl;

            if (inputFileStream.eof())
                cout << "Reached the end of file marker" << endl;
            else
                cout << "Error in input file" << endl;
        } else {
            cout << "Error opening input file, ";
            cout << "check 'input.txt' exists in correct directory" << endl;
        }


        inputFileStream.close();

        cout << "--reading from input.txt finished--" << endl << endl;
    }

    // reading from a text file using an input file stream object
    // this uses std::string
    {
        cout << "--reading from input.txt started--" << endl;

        ifstream inputFileStream;

        inputFileStream.open("input.txt");

        if (inputFileStream.good()) {
            cout << "Input file is good start processing" << endl;

            string inputString;

            inputFileStream >> inputString;

            while (!inputFileStream.fail()) {
                cout << inputString << ";";
                inputFileStream >> inputString;
            }

            cout << endl;

            if (inputFileStream.eof())
                cout << "Reached the end of file marker" << endl;
            else
                cout << "Error in input file" << endl;
        } else {
            cout << "Error opening input file, ";
            cout << "check 'input.txt' exists in correct directory" << endl;
        }

        inputFileStream.close();

        cout << "--reading from input.txt finished--" << endl << endl;
    }

    // reading from a text file using an input file stream object
    // this assumes the data in the text file is in the format of:
    // int double int double int double...
    {
        cout << "--reading from inputdata.txt started--" << endl;

        ifstream inputFileStream;

        inputFileStream.open("inputdata.txt");

        if (inputFileStream.good()) {
            int rowCounter = 1;
            int var1;
            double var2;

            inputFileStream >> var1;

            while (!inputFileStream.fail()) {
                cout << "row" << setw(3) << rowCounter;
                cout << "   var1 = " << setw(3) << var1;
                rowCounter++;

                inputFileStream >> var2;
                if (!inputFileStream.fail()) {
                    cout << "   var2 = " << setw(5) << var2;
                    inputFileStream >> var1;
                }
                cout << endl;
            }

            if (inputFileStream.eof())
                cout << "Reached the end of file marker" << endl;
            else
                cout << "Error whilst reading input file" << endl;
        } else {
            cout << "Error opening input file, ";
            cout << "check 'inputdata.txt' exists in correct directory" << endl;
        }

        inputFileStream.close();

        cout << "--reading from inputdata.txt finished--" << endl << endl;
    }

    cout << "End of program" << endl;

    return 0;
}