Saving Class Object to Binary File [duplicate]

Here is a very abstract idea of what you want, Write string size that helps to read string back for name, write age, again wite hobbies size that helps to read it again and finally write each string with it size. To read reverse the process,

#include <iostream>
#include <fstream>
#include <vector>

class User
{
private:
    std::string _name;
    int _age;
    std::vector<std::string> _hobbies;

public:
    std::string Name()
    { 
      return _name;
    }

    int Age()
    { 
      return _age;
    }

    std::vector<std::string> Hobbies()
    { 
      return _hobbies;
    }

    void Hobbies(std::string hobbieName)
    {
        _hobbies.push_back(hobbieName);
    }

    User(std::string name, int age)
    {
        _name = name;
        _age = age;
    }

    /**
     * @brief saves to user binary file
     * 
     * @param fout 
     */
    void save(std::ofstream &fout)
    {
        // write name
        size_t nsiz = this->_name.size();
        // write string size to read
        fout.write((const char *)(&nsiz), sizeof(nsiz));
        fout.write(&_name[0], nsiz);

        // write age
        fout.write((const char *)&_age, sizeof(int));

        // write hobbies size
        size_t hsiz = _hobbies.size();
        fout.write((const char *)&hsiz, sizeof(size_t));

        // write hobbies
        for (auto &str : _hobbies)
        {
            size_t ssiz = str.size();
            fout.write((const char *)(&ssiz), sizeof(ssiz));
            fout.write(&str[0], str.size());
        }
    }

    /**
     * @brief loads from binary file
     * 
     * @param fin 
     */
    void load(std::ifstream &fin)
    {
        // read name
        size_t nsiz = 0;
        fin.read((char*)&nsiz, sizeof(size_t));
        this->_name.resize(nsiz);
        fin.read(&_name[0], nsiz);

        // read age
        fin.read((char*)&_age, sizeof(int));

        // read hobbies size
        size_t hsiz = 0;
        fin.read((char*)(&hsiz), sizeof(hsiz));
        _hobbies.resize(hsiz);

        for(size_t i = 0; i < hsiz; ++i)
        {
            size_t ssiz = 0;
            fin.read((char*)&ssiz, sizeof(size_t));
            _hobbies[i].resize(ssiz);
            fin.read(&_hobbies[i][0], ssiz);
        }
    }
};

int main()
{
    User u1 = User("John", 48);

    u1.Hobbies("Art");
    u1.Hobbies("Lego");
    u1.Hobbies("Blogging");

    std::ofstream fout("data.bin", std::ofstream::binary);
    u1.save(fout);
    fout.close();

    User u2("", 0);

    std::ifstream fin("data.bin", std::ifstream::binary);
    u2.load(fin);
    fin.close();

    std::cout << u2.Name() << " with age " << u2.Age() << "'s Hobbies:\n";

    for (std::string hobbie : u2.Hobbies())
    {
        std::cout << hobbie << "\n";
    }
}

I hope that it helps, and make sure to do things what if string size is zero :)