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

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!