Mithat Konar (the wiki)

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====== File processing examples ======

===== File writing =====

==== Simple example ====

<file c++ simple-file-write.cpp>// This program writes data to a file.
#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    ofstream outfile;   // instantiate file pointer object
    outfile.open("public_radio.txt");   // associate file with file pointer object

    cout << "Writing to the file ... ";

    outfile << "KCMP\t" << 89.3 << endl;
    outfile << "KNOW\t" << 91.1 << endl;
    outfile << "KSJN\t" << 99.5 << endl;
    outfile.close();    // close the file!

    cout << "Done!" << endl;

    return 0;
}
</file>

==== Checking for opening errors ====

<file c++ simple-file-write2.cpp>// This program writes data to a file.
// Shows error checking.
#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    ofstream outfile;   // instantiate file pointer object
    outfile.open("public_radio.txt");   // associate file with file pointer object

    if (!outfile)
    {
        cout << "Error opening file." << endl;
        return 1;  // exit program with an error code
    }

    cout << "Writing to the file ... ";

    outfile << "KCMP\t" << 89.3 << endl;
    outfile << "KNOW\t" << 91.1 << endl;
    outfile << "KSJN\t" << 99.5 << endl;
    outfile.close();    // close the file!

    cout << "Done!" << endl;

    return 0;
}
</file>

==== Using filenames ====

<file c++ simple-file-write3.cpp>// This program writes data to a file.
// Converting string to c_str.
#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;

int main()
{
    ofstream outfile;   // instantiate file pointer object
    string filename;    // used to store filename to save file

    // get filename from user
    cout << "Enter the filename to store the file in\n"
         << "> ";
    cin >> filename;

    outfile.open(filename);            // associate file with file pointer object
    //outfile.open(filename.c_str());  // convert filename to C-string in pre-C++11

    if (!outfile)
    {
        cout << "Error opening file." << endl;
        return 1;  // exit program with an error code
    }

    cout << "Writing to the file ... ";

    outfile << "KCMP\t" << 89.3 << endl;
    outfile << "KNOW\t" << 91.1 << endl;
    outfile << "KSJN\t" << 99.5 << endl;
    outfile.close();    // close the file!

    cout << "Done!" << endl;

    return 0;
}
</file>

===== File reading =====

==== Simple example ====
<file c++ simple-file-read.cpp>// This program reads a number from a file.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main()
{
    string filename = "some_numbers.txt";
    int num1;

    ifstream infile;         // instantiate file pointer object
    infile.open(filename);   // associate file with file pointer object

    if (!infile)
    {
        cout << "Error opening file." << endl;
        return 1;  // exit program with error code
    }
    
    cout << "Reading from file ... ";

    infile >> num1;
    infile.close();    // close the file!

    cout << "Done!" << endl;
    cout << "The first number in the file is " << num1 << "." << endl;

    return 0;
}
</file>

==== Reading multiple tokens ====
<file c++ simple-file-read2.cpp>// This program reads two numbers from a file.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main()
{
    string filename = "some_numbers.txt";
    int num1, num2;

    ifstream infile;         // instantiate file pointer object
    infile.open(filename);   // associate file with file pointer object

    if (!infile)
    {
        cout << "Error opening file." << endl;
        return 1;  // exit program with error code
    }
    
    cout << "Reading from file ... ";

    infile >> num1 >> num2;
    infile.close();    // close the file!

    cout << "Done!" << endl;
    cout << "The first two numbers in the file are:" << endl
         << num1 << endl
         << num2 << endl
         << endl;

    return 0;
}
</file>

==== Read all tokens in a file ====
<file c++ simple-file-read3.cpp>// This program reads all the numbers from a file.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main()
{
    const string filename = "some_numbers.txt";
    int num1;

    ifstream infile;         // instantiate file pointer object
    infile.open(filename);   // associate file with file pointer object

    if (!infile)
    {
        cout << "Error opening file." << endl;
        return 1;  // exit program with error code
    }

    cout << "Reading from file ... " << endl;

    while (infile >> num1)
    {
        cout << num1 << endl;
    }
    infile.close();    // close the file!

    cout << "Done!" << endl;

    return 0;
}
</file>