PROBLEM : I am trying to write (binary writing) an object of Doubly Linked List onto File & write from it too. I have to write object's complete contents, then load it from file, and store it into new object to re-create the list in FIFO order. I thinking I am writing correctly, but I seriously have no idea how to load (read) it from file. REMEMBER: I am just trying to save and read CONTENTS of a node, & NOT POINTERS.
CODE::
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//template type BOOK class
template<class mytype>
class BOOK
{
private:
static int count; //declaration of static variable to set ID for books
public:
BOOK<mytype> *next, *prev; //BOOK type pointers; 'next' to store address of
next BOOK & 'prev' to store address of previous BOOK
int ID; //variable to store ID of a book
string bookName;//string to store name of a book
string author; //string to store name of author of book
string book_type;//string to store type of a book
long copies; //variable to store no. of copies a book
long price; //variable to store price of a book
string status; //to store status of a book, either its in stock or not
dynamicQueue<string> book_queue; //created an object of queueClass as data member of each Book
BOOK() //Constructor 0 argument to initialize everything
{
count++; //increment counter
ID=count; //assign counter to ID to be ID of newly added book
next = prev = 0; //Initializing both pointers to 0
bookName = "\0";
author = "\0";
book_type = "\0";
copies = price = 0;
status= "InStock";
}
BOOK(BOOK *n = 0, BOOK *p = 0, string book = "\0", string athr = "\0", string buk_type = "\0", long cp=0, long pr=0) //Constructor multiple arguments, to store information about a book
{
next = n; //store contents of user-given value n into next
prev = p; //store contents of user-given value p into previous
bookName = book;//store contents of user-given value book into bookName
author = athr; //store contents of user-given value athr into author
book_type = buk_type;//store contents of user-given value buk_type into book_type
copies = cp; //store contents of user-given value cp into copies
price = pr; //store contents of user-given value pr into price
status= "InStock";
count++; //increment counter
ID=count; //assign counter to ID to be ID of newly added book
}
};
template <class mytype> // declaration of
int BOOK<mytype>::count=0; // static variable to set ID for books
//--------------------
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Main Part for Adding a new Book.
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BookStoreDataBase<char> obj; //created object of Doubly linked list
string Book, Author, Booktype;
long Copies=1, Price=0;
cout<<"Enter Name of Book = "; cin>>Book;
cout<<"Enter Author = "; cin>>Author;
cout<<"Enter Type of Book = "; cin>>Booktype;
cout<<"Enter Number of Copies = "; cin>>Copies;
cout<<"Enter Price (PKR) = "; cin>>Price;
obj.addBook(Book, Author, Booktype, Copies, Price);
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Saving function to save all data to file
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template <class mytype>
void DoublyLinkedList<mytype>::save_data()
{
NODE<mytype> * temp = head; //made copy of head
fstream file; //created new file
file.open("mydata.txt", ios::binary | ios::out | ios::app);
while(temp->next!=0) //Until link list end
{
file.write(reinterpret_cast<char*>(&temp), sizeof(temp));
temp = temp - > next; //move temp to next node
}
file.write(reinterpret_cast<char*>(&temp), sizeof(temp)); //write again for last
//book's data
file.close();
}
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Now I have practically no idea on how to read the list from file, store contents into each node & with disturbing the saved arrangement, re-create the list in FIFO order. So I can print it later. I have practiced alot, gone to forums etc etc but not found any concrete Solution. Please help me out. Thanks in advance
A sample of my effort
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template <class mytype>
void DoublyLinkedList<mytype>::load_data()
{
fstream file;
file.open("mydata.txt", ios::binary | ios::in);
while(!file.eof())
{
NODE<mytype> *temp = new NODE<mytype>;
file.read(reinterpret_cast<char*>(&temp), sizeof(temp));
if(is_Empty())
{
head = tail = temp;
}
else
{
temp->prev->next = temp;
temp->next=0;
}
}
file.close();
}
//-------------------
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NO COMPILE TIME ERROR.
RUNTIME ERROR : Unhandled exception at 0x00CD8391 in DobulyList.exe: 0xC0000005: Access violation writing location 0x00000004.
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