We are trying to make Transaction class a private class within the Account_class, thus moving the whole definition of Transaction Classes operator inside the Transaction class. Im getting an error which says that Overloaded 'operator<<' must be a binary operator (has 3 parameters). How to make it work?

class Account_class {

friend ostream& operator<<(ostream& os, const Account_class& theAccount);

friend void readTransaction (vector & act_cl);

public:

Account_class(string& name, int account_number) : name(name), account_number(account_number){

}

void deposit(int amount) {

balance += amount;

Transaction transaction ("deposit", amount);

tr.emplace_back(transaction);

}

void withdrawal(int amount) {

balance -= amount;

if (balance < amount) {

cerr << "Insufficient Funds" << endl;

}

Transaction transaction ("withdrawal", amount);

tr.emplace_back(transaction);

}

private:

class Transaction {

friend ostream & operator << (ostream& transcation_os, const Transaction& theTransaction);

public:

Transaction(string type, int amount) : action(type), amount(amount) {}

// The error occurs in the following lines:

ostream & operator << (ostream& transcation_os, const Transaction& theTransaction) {

transcation_os << theTransaction.action << " " << theTransaction.amount << endl;

return transcation_os;

}

private:

string action;

int amount;

};