cppBinFilesAdvanced

#include <iostream>
#include <fstream>
#include <chrono>

struct Temp
{
    int id;
    double temperature;
    char desc[20];
};

int main()
{
    const int tempsSize{ 3 };
    Temp temps[tempsSize]{
        {1, 0,"ice"},
        {2, 100.0, "boil"},
        {3, 26.6, "comfort"}
    };


    std::fstream iofile;

    iofile.open("d:\\temp.dat", std::ios::trunc | std::ios::out | std::ios::in | std::ios::binary);

    if ( !iofile)
    {
        std::cout << "IOERROR: can't create/open file!\n";
        return 1;
    }

    for (int i{ 0 }; i < tempsSize; ++i)
    {
        iofile.write((char*)&(temps[i].id), sizeof(int));
        iofile.write((char*)&(temps[i].temperature), sizeof(double));
        iofile.write((char*)&(temps[i].desc), 20);
    }

    const int recordSize{ sizeof(int) + sizeof(double) + 20 };

    iofile.seekg(recordSize * 1, std::ios::beg);

    Temp fix{ 4, 100500.424242, "kipitok" };

    iofile.write((char*)&(fix.id), sizeof(int));
    iofile.write((char*)&(fix.temperature), sizeof(double));
    iofile.write((char*)&(fix.desc), 20);

    iofile.seekg(0, std::ios::beg);

    Temp readTemps[tempsSize]{};
    int idx{ 0 };

    while (!iofile.eof())
    {
        iofile.read((char*)&(readTemps[idx].id), sizeof(int));
        iofile.read((char*)&(readTemps[idx].temperature), sizeof(double));
        iofile.read((char*)&(readTemps[idx].desc), 20);
        if (iofile.fail())
        {
            break;
        }

        std::cout << "Temps #" << readTemps[idx].id << ' '
            << readTemps[idx].temperature << ' '
            << readTemps[idx].desc << '\n';
        ++idx;
    }

    iofile.close();

    return 0;
}