How to serialize and deserialize an object into/from binary files manually?

Question

I've been trying to write the below object into a file and got lot of trouble since strings are dynamically allocated.

class Student{
    string name, email, telephoneNo;
    int addmissionNo;
    vector<string> issued_books;
public:
    // There are some methods to initialize name, email, etc...
};

So I got to know that I can't just write into a file or read from a file an object with serialization. So I searched all over the internet about serialization with cpp and got to know about Boost library.But I wanted to do it my own (I know writing a library that already exist is not good, but I wanna see what's going on inside the code). So I got to know about overloading iostream << and >>. And I also know that serialize/deserialize into/from text.

But I want to serialize into a binary file. So I tried overloading ostream write and istream read. But then I got size issues(as write and read needs the sizeof the object it writes/reads).Then I also got to know about stringstream can help to serialize/deserialize objects into/from binary. But I don't how to do that?

So my real question is How to serialize and deserialize an object into/from binary files without third party libraries?

Answer 1

I have found a solution serialize and deserialize an object into/from a file. Here is an explaination

As I told you this is my class. And I have added two functions which overload the iostream's write and read.

class Student{
    string name, email, telephoneNo;
    int addmissionNo;
    vector<string> issuedBooks;
public:
    void create();  // initialize the private members
    void show();  // showing details

    // and some other functions as well...
    
    // here I'm overloading the iostream's write and read
    friend ostream& write(ostream& out, Student& obj);
    friend istream& read(istream& in, Student& obj);
};

But I have also told you that I have tried this already. The problem I have was how to read without object member's size. So I made changes as below (Please read comments also).

// write: overload the standard library write function and return an ostream
// @param out: an ostream
// @param obj: a Student object
ostream& write(ostream& out, Student& obj){
    // writing the objet's members one by one.
    out.write(obj.name.c_str(), obj.name.length() + 1); // +1 for the terminating '\0'
    out.write(obj.email.c_str(), obj.email.length() + 1);
    out.write(obj.telephoneNo.c_str(), obj.telephoneNo.length() + 1);
    out.write((char*)&obj.addmissionNo, sizeof(obj.addmissionNo)); // int are just cast into     a char* and write into the object's member
 
    // writing the vector of issued books   
    for (string& book: obj.issuedBooks){
        out.write(book.c_str(), book.length() + 1);
    }
    return out;
}
 
// read: overload the standard library read function and return an istream
// @param in: an istream
// @param obj: a Student object
istream& read(istream& in, Student& obj){
    // getline is used rather than read
    // since getline reads a whole line and can be give a delim character
    getline(in, obj.name, '\0');  // delimiting character is '\0' 
    getline(in, obj.email, '\0');
    getline(in, obj.telephoneNo, '\0');
    in.read((char*)&obj.addmissionNo, sizeof(int));

    for (string& book: obj.issuedBooks){
        getline(in, book, '\0');
    }
            return in;
}

As you can see I have wrote length+1 for the terminating '\0'. It is usefull in read function as we have used getline instead of read. So getline reads until the '\0'. So no need of a size. And here I'm writing and reading into/from a file.

void writeStudent(Student s, ofstream& f){
    char ch; // flag for the loop
    do{
        s.create(); // making a student        
        f.open("students", ios::app | ios::binary); // the file to be written
        write(f, s); // the overloaded function
        f.close();

        cout << "Do you want to add another record? (y/n): ";
        cin >> ch;
        cin.ignore();
    } while(toupper(ch) == 'Y'); // loop until user stop adding records. 
}

void readStudent(Student s, ifstream& f){
    char ch; // flag for the loop
    do{
        f.open("students", ios::in | ios::binary);
 
        cout << "Enter the account no of the student: ";
        int no;
        cin >> no;

        int found = 0;
        while (read(f, s)){
            if (s.retAddmissionNo() == no){
                found = 1;
                s.show();
            }
        }
        if (!found)
            cout << "Account Not found!\n";
 
        f.close();
        cout << "Do you want another record? (y/n): ";
        cin >> ch;
    } while(toupper(ch) == 'Y');
}

That's how I solved my problem. If something wrong here please comment. Thank you!