Cannot instantiate abstract class, but double checked overriding of virtual functions - c++

Question

I'm doing self-study C++. I tried a program from the book, that would normally allocate a few objects of two derived classes dynamically using an array of pointers. I'm however preparing for an assignment where I'm not allowed to use pointers, so I made an alternative version without pointers.
The only error it gives me is C2259 "cannot instantiate abstract class", but I'm pretty sure I have overriden all the virtual functions.
Here is the header:
#ifndef ACCTBAC_H_
#define ACCTBAC_H_
#include <iostream>
#include <string>
// Abstract Base Class
class AcctABC
{
private:
std::string fullName;
long acctNum;
double balance;
protected:
struct Formatting
{
std::ios_base::fmtflags flag;
std::streamsize pr;
};
const std::string& FullName() const { return fullName; }
long AcctNum() const { return acctNum; }
Formatting SetFormat() const;
void Restore(Formatting& f) const;
public:
AcctABC(const std::string& s = "Nullbody", long an = -1, double bal = 0.0);
void Deposit(double amt);
virtual void Withdraw(double amt) = 0; // pure virtual function
double Balance() const { return balance; };
virtual void ViewAcct() const = 0; // pure virtual function
virtual ~AcctABC() {}
};
// Brass Account Class
class Brass : public AcctABC
{
public:
Brass(const std::string& s = "Nullbody", long an = -1, double bal = 0.0) : AcctABC(s, an, bal) {}
virtual void Withdraw(double amt);
virtual void ViewAcct() const;
virtual ~Brass() {}
};
// Brass Plus Account Class
class BrassPlus : public AcctABC
{
private:
double maxLoan;
double rate;
double owesBank;
public:
BrassPlus(const std::string& s = "Nullbody", long an = -1, double bal = 0.0, double ml = 500, double r = 0.10);
BrassPlus(const Brass& ba, double ml = 500, double r = 0.1);
virtual void ViewAcct() const;
virtual void Withdraw(double amt);
void ResetMax(double m) { maxLoan = m; }
void ResetRate(double r) { rate = r; }
void ResetOwes() { owesBank = 0; }
};
#endif
the class functions:
// acctabc.cpp -- bank account class methods
#include <iostream>
#include "acctabc.h"
using std::cout;
using std::ios_base;
using std::string;
// Abstract Base Class
AcctABC::AcctABC(const string& s, long an, double bal)
{
fullName = s;
acctNum = an;
balance = bal;
}
void AcctABC::Deposit(double amt)
{
if (amt < 0)
cout << "Negative deposit not allowed; "
<< "deposit is cancelled.\n";
else
balance += amt;
}
void AcctABC::Withdraw(double amt)
{
balance -= amt;
}
// protected methods for formatting
AcctABC::Formatting AcctABC::SetFormat() const
{
// set up ###.## format
Formatting f;
f.flag = cout.setf(ios_base::fixed, ios_base::floatfield);
f.pr = cout.precision(2);
return f;
}
void AcctABC::Restore(Formatting& f) const
{
cout.setf(f.flag, ios_base::floatfield);
cout.precision(f.pr);
}
// Brass methods
void Brass::Withdraw(double amt)
{
if (amt < 0)
cout << "Withdrawal amount must be positive; "
<< "withdrawal cancelled.\n";
else if (amt <= Balance())
AcctABC::Withdraw(amt);
else
cout << "Withdrawal amount of $" << amt
<< " exceeds your balance.\n"
<< "Withdrawal cancelled.\n";
}
void Brass::ViewAcct() const
{
Formatting f = SetFormat();
cout << "Brass Client: " << FullName() << "\n";
cout << "Account Number: " << AcctNum() << "\n";
cout << "Balance: $" << Balance() << "\n";
Restore(f);
}
// BrassPlus methods
BrassPlus::BrassPlus(const string& s, long an, double bal, double ml, double r) : AcctABC(s, an, bal)
{
maxLoan = ml;
owesBank = 0.0;
rate = r;
}
void BrassPlus::ViewAcct() const
{
Formatting f = SetFormat();
cout << "BrassPlus Client: " << FullName() << "\n";
cout << "Account Number: " << AcctNum() << "\n";
cout << "Balance: $" << Balance() << "\n";
cout << "Maximum loan: $" << maxLoan << "\n";
cout << "Owed to bank: $" << owesBank << "\n";
cout.precision(3);
cout << "Loan Rate: " << 100 * rate << "%\n";
Restore(f);
}
void BrassPlus::Withdraw(double amt)
{
Formatting f = SetFormat();
double bal = Balance();
if (amt <= bal)
AcctABC::Withdraw(amt);
else if (amt <= bal + maxLoan - owesBank)
{
double advance = amt - bal;
owesBank += advance * (1.0 + rate);
cout << "Bank Advance: $" << advance << "\n";
cout << "Finance charge: $" << advance * rate << "\n";
Deposit(advance);
AcctABC::Withdraw(amt);
}
else
cout << "Credit limit exceeded. Transaction cancelled.\n";
Restore(f);
}
and the main program:
// usebrass3.cpp -- polymorphic example using an abstract base class
#include <iostream>
#include <string>
#include "acctabc.h"
#include <vector>
const int CLIENTS = 4;
int main()
{
using std::cin;
using std::cout;
using std::vector;
using std::string;
vector<AcctABC> accounts(CLIENTS);
string temp;
long tempnum;
double tempbal;
char kind;
for (int i = 0; i < CLIENTS; i++)
{
cout << "Enter client's name: ";
getline(cin, temp);
cout << "Enter client's account number: ";
cin >> tempnum;
cout << "Enter opening balance: $";
cin >> tempbal;
cout << "Enter 1 for Brass Account: ";
while (cin >> kind && (kind != '1' && kind != '2'))
cout << "Enter either 1 or 2: ";
if (kind == 1)
accounts.push_back(Brass(temp, tempnum, tempbal));
else
{
double tmax, trate;
cout << "Enter the overdraft limit: $";
cin >> tmax;
cout << "Enter the interest rate "
<< "as a decimal fraction: ";
cin >> trate;
accounts.push_back(BrassPlus(temp, tempnum, tempbal, tmax, trate));
}
while (cin.get() != '\n')
continue;
}
cout << "\n";
for (int i = 0; i < CLIENTS; i++)
{
accounts[i].ViewAcct();
cout << "\n";
}
cout << "Done.\n";
return 0;
}

Answer 1

Here:
vector<AcctABC> accounts(CLIENTS);
you are trying to create a vector of AcctABC with CLIENTS default constructed AcctABC elements. But you cannot have AcctABC elements when the class is abstract. You also cannot have Brass elements in a vector of AcctABCs. You need pointers when you want to store a polymorphic type in a vector.

Answer 2

You cannot do this
vector<AcctABC> accounts(CLIENTS);
because it will make CLIENTS number of default constructed abstract base classes. You will also lose polymorphism and induce object slicing. Instead
vector<std::unique_ptr<AcctABC>> accounts;
then for example
accounts.push_back(std::make_unique<Brass>(temp, tempnum, tempbal));