https://www.gamingonlinux.com/forum/topic/1689?page=1#r5195

#include <iostream> // cout, cerr
#include <fstream>  // ifstream, ofstream, getline()
#include <cstring>  // strncmp()
#include <unistd.h> // getlogin_r()

using namespace std;

typedef struct {
    unsigned short right;
    unsigned short throttle;
    unsigned short left;
    unsigned short brake;
    unsigned short frontWeapon1;
    unsigned short frontWeapon2;
    unsigned short frontWeapon3;
    unsigned short extra;
    unsigned short rearWeapon;
} KeySettings;

class MiniCarRacingKeyControler {
private:
    string pathToFile;
    string fullData;

public:
    MiniCarRacingKeyControler (string pathToFile) : pathToFile(pathToFile) {}

    ~MiniCarRacingKeyControler() /* throw() */ {}

    void readData () {
        // Getting whole file information.

            ifstream file(pathToFile);

            if (file.is_open() == false)
                throw (runtime_error("MiniCarRacingKeyControler::readData(): file " + pathToFile + " cannot be opened for reading!"));

            string rawData;

            while (getline(file, rawData)) {
                if (fullData.size() > 0)
                    fullData += '\n';

                fullData += rawData;
            }

            file.close();
    }

    void saveData () const {
        // Saving full data to file.

            ofstream file(pathToFile);

            if (file.is_open() == false)
                throw (runtime_error("MiniCarRacingKeyControler::saveData(): file " + pathToFile + " cannot be opened for writing!"));

            file << fullData;

            file.close();
    }

    void setPlayerControls (const string& playerName, KeySettings keySettings) {
        // We'll have to compare those variables more than 10k times, why not save them to temporaries?

            unsigned int fullDataSize = fullData.size();
            const char* playerNameCStr = playerName.c_str();
            unsigned int playerNameSize = playerName.size();

        // Searching for byte where player data begins.

            unsigned int playerDataIndex = 0;

            for (unsigned int i = 0; i < fullDataSize; ++i) {
                if (!strncmp(playerNameCStr, &fullData[i], playerNameSize)) {
                    playerDataIndex = i;
                    break;
                }
            }

            if (playerDataIndex == 0)
                throw (runtime_error("MiniCarRacingKeyControler::setPlayerControls(): there is no player called " + playerName + "!"));

        // Rewriting keyboard controls bytes.

        /*
         *  NAME            BYTE
         *  Right           22
         *  Throttle        34
         *  Left            46
         *  Brake           58
         *  Front Weapon 1  70
         *  Front Weapon 2  82
         *  Front Weapon 3  94
         *  Extra           106
         *  Rear Weapon     118
        */

            fullData[playerDataIndex + 21  ] = keySettings.right;
            fullData[playerDataIndex + 33  ] = keySettings.throttle;
            fullData[playerDataIndex + 45  ] = keySettings.left;
            fullData[playerDataIndex + 57  ] = keySettings.brake;
            fullData[playerDataIndex + 69  ] = keySettings.frontWeapon1;
            fullData[playerDataIndex + 81  ] = keySettings.frontWeapon2;
            fullData[playerDataIndex + 93  ] = keySettings.frontWeapon3;
            fullData[playerDataIndex + 105 ] = keySettings.extra;
            fullData[playerDataIndex + 117 ] = keySettings.rearWeapon;
    }

    bool checkIfPlayerExists (const string& playerName) {
        unsigned int fullDataSize = fullData.size();
        const char* playerNameCStr = playerName.c_str();
        unsigned int playerNameSize = playerName.size();

        for (unsigned int i = 0; i < fullDataSize; ++i) {
            if (!strncmp(playerNameCStr, &fullData[i], playerNameSize)) {
                return true;
            }
        }

        return false;
    }

    // Accesor methods.

    const string& getPathToFile () const {
        return pathToFile;
    }

    void setPathToFile (string& newPathToFile) {
        pathToFile = newPathToFile;
    }

    const string& getFullData () const {
        return fullData;
    }


};

int main (int argc, char** argv) {
    // Getting data.

        string pathToFile;

        if (argc >= 2)
            pathToFile = argv[1];

        else {
            char login[100];

            getlogin_r(login, 100);

            pathToFile = "/home/";
            pathToFile += login;
            pathToFile += "/.wine/drive_c/windows/MiniCarRacing.ini";
        }

        MiniCarRacingKeyControler controler(pathToFile);

        controler.readData();

    // Menu.

        string playerName;

        cout << "Player name: ";
            cin >> playerName;

        if (controler.checkIfPlayerExists(playerName) == false)
            throw (runtime_error("main(): there is no player called " + playerName + "!"));

        KeySettings keySettings;
            cout << "Right: ";
                cin >> keySettings.right;

            cout << "Throttle: ";
                cin >> keySettings.throttle;

            cout << "Left: ";
                cin >> keySettings.left;

            cout << "Brake: ";
                cin >> keySettings.brake;

            cout << "Front Weapon 1: ";
                cin >> keySettings.frontWeapon1;

            cout << "Front Weapon 2: ";
                cin >> keySettings.frontWeapon2;

            cout << "Front Weapon 3: ";
                cin >> keySettings.frontWeapon3;

            cout << "Extra: ";
                cin >> keySettings.extra;

            cout << "Rear Weapon: ";
                cin >> keySettings.rearWeapon;

    // Saving controls.

        controler.setPlayerControls("Jezor", keySettings);

        controler.saveData();

    // Exited cleanly.

        cout << "Player data saved successfully!" << endl;

        return 0;
}