Thread: hey all for the second time this week

here's the deal. i tried implementing classes in the way that i was questioning the other day, and here's the code i got:

Code:

#ifndef LOGIN_H
#define LOGIN_H

#include <iostream>
#include <fstream.h>
#include <string>
#include <stdlib.h>
#include <ctype.h>

using namespace std;

class BankClass
{
 private:
 double balance;

 public:
 class BalanceOps
 {
  public:
  BalanceOps ()
  {
   balance = 0.0;
  }
  void credit (double amt)
  {
   balance += amt;
  }
  void debit (double amt)
  {
   balance -= amt;
  }
  double getBalance ()
  {
   return balance;
  }
  void setBalance (double amt)
  {
   balance = amt;
  }
 };
 class FileOpsBank
 {
  private:
  string username;
  string usersdir;
  double balance;

  public:
  FileOpsBank (string user, string dir)
  {
   username = user;
   usersdir = dir;
  }
  void loadBalance (string filename)
  {
   ifstream infile;
   string tempstr;

   infile.open(filename.c_str());
   getline (infile, tempstr);
   infile.close ();
   balance = strtod (tempstr.c_str(), NULL);
  }
  void saveBalance (string filename)
  {
   ofstream outfile;
   outfile.open (filename.c_str());
   outfile << balance;
   outfile.close ();
  }
 };
};

int main ()
{
 BankClass::BalanceOps banker;
 double amt;

 banker.setBalance (2.25);
 cin >> amt;
 banker.credit (amt);
 amt = banker.getBalance ();
 cout << amt;
 system ("pause");
 return 0;
}

#endif

the main function here was just to test the class, not my actual program. Anyways, when i compile the code as is with Dev C++, it says "linker error: undefined reference to BankClass::balance". What is going on here? oh, and i know i have a bunch of unneccesary libraries included, i promise, im using them later.

Your code has many issues.

1. Just because a class is embedded in another class, does not mean it has access to that class' private members. You could solve this by making it a friend class.

2. In the embedded classes you can't just reference balance unqualified. It will look for it's own member called balance, which ofcourse doesn't exist. However you can't say BankClass::balance either as this is treated as a static variable. You need a way to say this->balance where "this" means BankClass and not BalanceOps, but nothing like this exist. The best way to solve this is pass in a instance of BankClass, to each function that needs it, though this is not the best overall solution.

3. Finally, when you instance your BalanceOps class with BankClass::BalanceOps banker; A BankClass is not automatically created. BankClass and BalanceOps are 2 different entities and are not linked in anyway.

Basically it boils down to the 1st point I made, embeded class don't gain any special access or abilities by being embeded. Think of a class defined in a class as just a typedef and nothing more.

By the way, "hey all" is not a good topic title. Try to shortly outline your issue instead.

As for the issues in your code: you didn't pick up a single word I wrote in your last thread, did you?

Yes, there is. What if you want more than one bank?

Also, your code looks like it's meant to be in a header file. You shouldn't put function implementations like main() in header files if you can help it.

I'm sure that someone has mentioned this, but

Code:

#include <fstream.h>

should be <fstream>. Changing <stdlib.h> to <cstdlib> and <ctype.h> to <cctype> would probably be a good idea too, but not essential.