Append Function Does not Working Filing c++

i want to save book data to a file. Wrote code given below. Code below is working fine on my personal system, but it is overwriting previous file data on some other systems.

class Book
{
private:
    int id, price;
public:
    void inp()
    {
        cin >> id >> price;
    }
    void disp()
    {
        cout << "id = " << id << "\nPrice = " << price << endl;
    }
};
void Write()
{
    ofstream of;
    Book b;
    b.inp();
    of.open("b.dat",ios::binary | ios::app );
    of.write((char*)&b, sizeof(Book));
    of.close();
}

enter code here