抽象基类（ABC）

被调用方法为虚拟，所以根据调方法的对象类型来判断，使用合适的成员函数

//////////////////////////////////////////////////////
///////////////////main.cpp///////////////////////////
// usebrass3.cpp -- polymorphic example, abstract base class
// compile with brass.cpp
#include <iostream>
#include "acctabc.h"
const int CLIENTS = 4;
const int LEN = 40;
int main()
{
   using std::cin;
   using std::cout;
   using std::endl;
   AcctABC * p_clients[CLIENTS];
  
   int i;
   for (i = 0; i < CLIENTS; i++)
   {
       char temp[LEN];
       long tempnum;
       double tempbal;
       char kind;
       cout << "Enter client's name: ";
       cin.getline(temp, LEN);
       cout << "Enter client's account number: ";
       cin >> tempnum;
       cout << "Enter opening balance: $";
       cin >> tempbal;
       cout << "Enter 1 for Brass Account or "
            << "2 for BrassPlus Account: ";
       while (cin >> kind && (kind != '1' && kind != '2'))
           cout <<"Enter either 1 or 2: ";
       if (kind == '1')
           p_clients[i] = new 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;
           p_clients[i] = new BrassPlus(temp, tempnum, tempbal,
                                        tmax, trate);
        }
        while (cin.get() != '\n')
            continue;
   }
   cout << endl;
   for (i = 0; i < CLIENTS; i++)
   {
       p_clients[i]->ViewAcct();
       cout << endl;
   }
             
   for (i = 0; i < CLIENTS; i++)
   {
       delete p_clients[i];  // free memory
   }
   cout << "Done.\n";        
 
   return 0;
}

 

 

///////////////////////////////////////////////////
////////////////acctabc.h//////////////////////////
// acctabc.h  -- bank account classes
#ifndef ACCTABC_H_
#define ACCTABC_H_

// Abstract Base Class
class AcctABC
{
private:
    enum {MAX = 35};
    char fullName[MAX];
    long acctNum;
    double balance;
protected:                     //共有继承的类可以直接调用保护成员，但不能直接调用私有成员
    const char * FullName() const {return fullName;}
    long AcctNum() const {return acctNum;}
    std::ios_base::fmtflags SetFormat() const;
public:
    AcctABC(const char *s = "Nullbody", long an = -1,
                double bal = 0.0);
    void Deposit(double amt) ;
    virtual void Withdraw(double amt) = 0; // pure virtual function 纯虚拟函数可以不写在定义中
    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 char *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 char *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

 

 

////////////////////////////////////////////////////////
///////////acctabc.cpp//////////////////////////////////
// acctabc.cpp -- bank account class methods
#include <iostream>
#include <cstring>
using std::cout;
using std::ios_base;
using std::endl;

#include "acctabc.h"

// Abstract Base Class
AcctABC::AcctABC(const char *s, long an, double bal)
{
    strncpy(fullName, s, MAX - 1);
    fullName[MAX - 1] = '\0';
    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 method
ios_base::fmtflags AcctABC::SetFormat() const
{
 // set up ###.## format
    ios_base::fmtflags initialState =
        cout.setf(ios_base::fixed, ios_base::floatfield);
    cout.setf(ios_base::showpoint);
    cout.precision(2);
    return initialState;
}

// Brass methods
void Brass::Withdraw(double amt)
{
    if (amt < 0)
        cout << "Withdrawal amount must be positive; "
             << "withdrawal canceled.\n";
    else if (amt <= Balance())
        AcctABC::Withdraw(amt);
    else
        cout << "Withdrawal amount of $" << amt
             << " exceeds your balance.\n"
             << "Withdrawal canceled.\n";
}

void Brass::ViewAcct() const
{
  
    ios_base::fmtflags initialState = SetFormat();
    cout << "Brass Client: " << FullName() << endl;
    cout << "Account Number: " << AcctNum() << endl;
    cout << "Balance: $" << Balance() << endl;
    cout.setf(initialState);
}

// BrassPlus Methods
BrassPlus::BrassPlus(const char *s, long an, double bal,
           double ml, double r) : AcctABC(s, an, bal)
{
    maxLoan = ml;
    owesBank = 0.0;
    rate = r;
}

BrassPlus::BrassPlus(const Brass & ba, double ml, double r)
           : AcctABC(ba)   // uses implicit copy constructor
{
    maxLoan = ml;
    owesBank = 0.0;
    rate = r;
}

void BrassPlus::ViewAcct() const
{
    ios_base::fmtflags initialState = SetFormat();

    cout << "BrassPlus Client: " << FullName() << endl;
    cout << "Account Number: " << AcctNum() << endl;
    cout << "Balance: $" << Balance() << endl;
    cout << "Maximum loan: $" << maxLoan << endl;
    cout << "Owed to bank: $" << owesBank << endl;
    cout << "Loan Rate: " << 100 * rate << "%\n";
    cout.setf(initialState);
}

void BrassPlus::Withdraw(double amt)
{
    ios_base::fmtflags initialState = 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 << endl;
        cout << "Finance charge: $" << advance * rate << endl;
        Deposit(advance);
        AcctABC::Withdraw(amt);
    }
    else
        cout << "Credit limit exceeded. Transaction cancelled.\n";
    cout.setf(initialState);
}