Writing and reading objects to and from file - c++

Question

I have a class User with two std::string attributes. When i try to read it from file i got exception from uxitility from line 222:
(*_Pnext)->_Myproxy = nullptr;
It happens after function isUserInFile()
Some peaces of my code:
Class User {
protected:
std::string login;
std::string password;
public:
friend std::istream&operator>>(std::istream&in, User &obj) {
//std::cout << "Логин: "; //"Login: "
in >> obj.login;
//std::cout << "Пароль: "; //"Password: "
in >> obj.password;
return in;
}
friend std::ostream&operator<<(std::ostream&out, User&obj) {
out << obj.login << " " << obj.password;
return out;
}
void encrypt() {
char key[3] = { 'K','E','Y' };
std::string buf = password;
for (int i = 0; i < buf.size(); i++)
buf[i] = password[i] ^ key[i % (sizeof(key) / sizeof(char))];
password = buf;
//buf.clear();
}
bool isUserInFile() {
User user;
std::ifstream file;
file.open("Users.txt");
while (!file.eof() && file.read((char*)&user, sizeof(User)))
if (login == user.login) {
file.close();
return true;
}
file.close();
return false;
}
};
bool registration() {
User user;
std::fstream file;
file.open("Users.txt", std::ios::in | std::ios::out | std::ios::app);
std::cout << "Регистрация:\n"; //"Registration:\n"
std::cin >> user;
user.encrypt();
if (!user.isUserInFile()) {
file.write((char*)&user, sizeof(User));
file.close();
return true;
}
std::cout << "Пользователь с данным логином уже существует\n"; //"User with this login already exists\n"
file.close();
system("pause");
return false;
}

Answer 1

Comments went in the correct direction to show where the problem is. But the solution is much simpler, you already have your stream operators, so just use them!
To write into the file you can use:
file << user << std::endl;
and then to read you simply:
file >> user;
For this to keep working you will need some things:
A user should never enter a white-space anywhere in their password.
You need to ensure that the writing and reading is always done in the same order.
Alternatively you can create a conversion from string and to string along the lines of:
static const char SEP1 = ' ', SEP2 = '\r';
friend std::string to_string(const User& u)
{
std::string result = u.login + SEP1 + u.password + SEP2;
return result;
}
explicit User(std::string line)
{
size_t pos1 = s.find(SEP1);
size_t pos2 = s.find(SEP2, pos1);
login = s.substr(0, pos1);
password = s.substr(pos1+1, pos2-pos1);
}
Then you can in your main you can read a block of data and simply construct a user from it, alternatively you can convert a user into a string before writing. A beauty of this approach is that you select the separators and they are stable between functions.