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Nov 7th, 2008

Pointers, Arrays and Creating Objs...

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Btw below is the key parts of my code - not all as there are loads of lines:

C++ Syntax (Toggle Plain Text)
//main.cpp
#include <iostream>
#include "Customer.h"
 
using namespace std;
 
void displayMainMenu();
int enterMainChoice();
void displayAccountMenu();
int enterAccountChoice();
int enterCustomerID();
Customer createCustomer();
 
void main(void)
{
	unsigned short numberOfCustomers = 0;
	Customer *Customers[10];
 
	*Customers[numberOfCustomers] = createCustomer();
	numberOfCustomers++;
}
 
Customer createCustomer()
{
	string name;
	int age;
	cout << "\nPlease enter you name: ";
	cin >> name;
	cout << "Please enter you age: ";
	cin >> age;
	return Customer(name, age);
}
//main.cpp
#include <iostream>
#include "Customer.h"

using namespace std;

void displayMainMenu();
int enterMainChoice();
void displayAccountMenu();
int enterAccountChoice();
int enterCustomerID();
Customer createCustomer();

void main(void)
{
	unsigned short numberOfCustomers = 0;
	Customer *Customers[10];

	*Customers[numberOfCustomers] = createCustomer();
	numberOfCustomers++;
}

Customer createCustomer()
{
	string name;
	int age;
	cout << "\nPlease enter you name: ";
	cin >> name;
	cout << "Please enter you age: ";
	cin >> age;
	return Customer(name, age);
}

----------------
Below is just the main function from Customer.cpp
----------------

C++ Syntax (Toggle Plain Text)
Customer::Customer(string name, int age)
{
	this->name = name;
	this->age = age;
}
Customer::Customer(string name, int age)
{
	this->name = name;
	this->age = age;
}

Now it almost works. I can run it and it asks me for the information, but when it tries to add the actual customer is crashes in "xstring" with this error:

Unhandled exception at 0x643924f0 (msvcp90d.dll) in bankusingarrays.exe: 0xC0000005: Access violation reading location 0xcccccce8.

Now - I thought it would be because I am passing back something which can't be then put into the pointer array.

But I am not sure how to go about it - trying to create the object and store the address in the pointer array. I am pretty new with C++ so try and bare with me lol..

Thanks!

Lokolo

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Nov 7th, 2008

Re: Pointers, Arrays and Creating Objs...

C++ Syntax (Toggle Plain Text)
Customer *Customers[10];
Customer *Customers[10];

You create an array of pointers to that object.

Why don't you do:

C++ Syntax (Toggle Plain Text)
 
Customer Customers[10];
Customer[numberOfCustomers] = createCustomer();
Customer Customers[10];
Customer[numberOfCustomers] = createCustomer();

-------------

1.Basically you are misuing pointers. In C and C++, when a variable is uninitialized, it contains a garbage value. Thus, Customers from 0 to 9 point to garbage values. They are pointers, which means they point in unknown places in the memory.

Then, you are assigning a value to that unknown memory location. This is the error. Before assigning, you have to be sure that the pointer points to a valid memory location of that object.
This is what you are doing.

C++ Syntax (Toggle Plain Text)
int main()
{
	int *p, x;
 
	x = 10;
	*p = x;
}
int main()
{
	int *p, x;

	x = 10;
	*p = x;
}

This is what you should be doing.

C++ Syntax (Toggle Plain Text)
int main()
{
	int *p, x;
 
	x = 10;
	p = &x;
}
int main()
{
	int *p, x;

	x = 10;
	p = &x;
}

If you still want an array of pointers to Customer objects, you should write:

C++ Syntax (Toggle Plain Text)
Customers[numberOfCustomers] = &(createCustomer()); //the address of the object
Customers[numberOfCustomers] = &(createCustomer()); //the address of the object

2.
Don't use void main(void). Just int main(). The use of void in the parentheses is redundant. It is required in C but not in C++.

Last edited by minas1; Nov 7th, 2008 at 1:49 pm.

minas1

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Nov 7th, 2008

Re: Pointers, Arrays and Creating Objs...

Hi
could u please post the Customer.h too?

sidatra79

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Nov 7th, 2008

Re: Pointers, Arrays and Creating Objs...

Click to Expand / Collapse Quote originally posted by sidatra79 ...

Hi
could u please post the Customer.h too?

C++ Syntax (Toggle Plain Text)
#include <string>
#pragma once
 
using namespace std;
//----------------------
class Customer
{
 
private:
	string name;
	int age;
 
public:
 
	//builder
	Customer(string name, int age);
 
	//operations
	void Display();
};
#include <string>
#pragma once

using namespace std;
//----------------------
class Customer
{

private:
	string name;
	int age;

public:
	
	//builder
	Customer(string name, int age);

	//operations
	void Display();
};

the display function doesn't have anything it btw, thats for later

Quote originally posted by minas1 ...

...

Ok thanks dude, briefly looking at it makes total sense, will look over my code to do as you say!

Lokolo

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Nov 7th, 2008

Re: Pointers, Arrays and Creating Objs...

Hi again,
have a look on this it might help u:

c++ Syntax (Toggle Plain Text)
#include <string>
#include <iostream>
 
using namespace std;
 
const int MAX_NO_OF_CUSTOMERS = 3;
 
class Customer
{
private:
	string name;
	int age;
	static unsigned short numberOfCustomers;
public:
	Customer()
	{
		createCustomer();	
		numberOfCustomers++;
	}
 
	Customer(string name, int age)
	{
		this->name = name;
		this->age = age;	
	}
 
	Customer createCustomer()
	{
		string name;
		int age;
		cout << "\nPlease enter you name: ";
		cin >> name;
		cout << "Please enter you age: ";
		cin >> age;
		return Customer(name, age);	
	}
	int getNumberofCustomers()
	{
		return numberOfCustomers;
	}
};
unsigned short Customer::numberOfCustomers = 0;
 
 
int main()
{
	int customersInTotal;
	Customer *Customers = new Customer[MAX_NO_OF_CUSTOMERS];
	customersInTotal=Customers->getNumberofCustomers();
	cout<<"Until now "<<customersInTotal<<" customers have been added."<<endl;
	return 0;
}
#include <string>
#include <iostream>

using namespace std;

const int MAX_NO_OF_CUSTOMERS = 3;

class Customer
{
private:
	string name;
	int age;
	static unsigned short numberOfCustomers;
public:
	Customer()
	{
		createCustomer();	
		numberOfCustomers++;
	}

	Customer(string name, int age)
	{
		this->name = name;
		this->age = age;	
	}

	Customer createCustomer()
	{
		string name;
		int age;
		cout << "\nPlease enter you name: ";
		cin >> name;
		cout << "Please enter you age: ";
		cin >> age;
		return Customer(name, age);	
	}
	int getNumberofCustomers()
	{
		return numberOfCustomers;
	}
};
unsigned short Customer::numberOfCustomers = 0;


int main()
{
	int customersInTotal;
	Customer *Customers = new Customer[MAX_NO_OF_CUSTOMERS];
	customersInTotal=Customers->getNumberofCustomers();
	cout<<"Until now "<<customersInTotal<<" customers have been added."<<endl;
	return 0;
}

i did on a hurry....maybe there are big mistakes

However it compiles and runs...

P.S: keep this in mind:
A no-argument constructor will be called automatically when dealing with an array of objects. But when u define some constructor with arguments, then u need to define a no-argument constructor too.

Last edited by sidatra79; Nov 7th, 2008 at 3:52 pm. Reason: added sth

sidatra79

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Nov 7th, 2008

Re: Pointers, Arrays and Creating Objs...

Have you tried what I told you?

minas1

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