File I/O in C++ - Having some trouble writing back data? - c++

Question

This project is a basic ATM program. I'm using a file to store all the account details. So, every time I run the .exe file, It will read the data from the file and insert it into an AVL tree. And when I close the program, all the data in the AVL nodes will be inserted back into the file.
Data is stored in the file in this order (Each separated by a newline char) ID, Password, Name, Add, City, Pin, Balance.
Sample file --
12
4576
Vert
No_999,GoLane
Dallas
89777
50000
16
2342
Nerd
No_888,FoLane
Chicago
89999
30000
The problem is I cannot write back data into the file. Any suggestions please?
P.S. Please excuse my inline class methods please...
Program--
#include<iostream>
#include<conio.h>
#include<string.h>
#include<fstream>
using namespace std;
fstream file("one2.txt",ios::in|ios::out);//Opening the file 'one2.txt' in global scope
//AVL tree code starts here
class avl
{
struct node //The structure node which is going to hold the data sets in the tree
{
int id,pwd;
char name[15],add[30],city[10];
int pn;
double bal;
node *left, *right;
int height;
//node constructors
node(int i,int p,char nam[15], char a[30], char c[10],int pin,double b, node * l,node * r,int h)
{
id=i;
pwd=p;
strcpy(name,nam);
strcpy(add,a);
strcpy(city,c);
pn=pin;
bal=b;
left=l;
right=r;
height=h;
}
node()
{
left=right=NULL;
id=pwd=pn=0;
bal=0;
height=-1;
}
};
node *root;
node *nullnode;
int Height(node *t)const //Func to return the height of a node
{
return((t==NULL)? -1:t->height);
}
int max(int a,int b)
{
return(a>b)?a:b;
}
//Beginning of Insert() -- To create and insert data into the nodes
void insert(const int &x,int p, char nam[15], char a[30], char c[10],int pin,double b, node *&t)
{
if(t==NULL)
t = new node(x,p,nam,a,c,pin,b,NULL,NULL,-1);
else if(x<t->id)
{
insert(x,p,nam,a,c,pin,b,t->left);
if(Height(t->left) - Height(t->right)==2)
{
if(x<t->left->id)
single_rotate_with_left(t);
else
double_rotate_with_left(t);
}
}
else if(x>t->id)
{
insert(x,p,nam,a,c,pin,b,t->right);
if(Height(t->right)-Height(t->left)==2)
{
if(x>t->right->id)
single_rotate_with_right(t);
else
double_rotate_with_right(t);
}
}
else
t->height=max(Height(t->left),Height(t->right)+1);
}
//End of insert()
//Func to print the node data. Just a sample to check if all the data
// were inserted into the tree
//Inorder traversal
void print(node *&t)
{
if(t!=NULL)
{
print(t->left);
cout<<endl;
cout<<"ID "<<t->id<<" Name "<<t->name;
cout<<endl<<t->pwd<<endl<<t->add<<"\n"<<t->city;
cout<<"-"<<t->pn<<endl<<t->bal<<endl;
print(t->right);
}
}
//Think there's gonna be no problem with the rotation and other AVL tree func codes.
//Beginning of AVL rotations
void single_rotate_with_left(node *&k2)
{
node *k1=k2->left;
k2->left=k1->right;
k1->right=k2;
k2->height=max(Height(k2->right),Height(k2->left))+1;
k1->height=max(Height(k1->left),(k2->height))+1;
k1=k2;
}
void single_rotate_with_right(node *&k2)
{
node *k1=k2->right;
k2->right=k1->left;
k1->left=k2;
k2->height=max(Height(k2->left),Height(k2->right))+1;
k1->height=max(Height(k1->right),(k2->height))+1;
k1=k2;
}
void double_rotate_with_left(node *&a)
{
single_rotate_with_right(a->left);
single_rotate_with_left(a);
}
void double_rotate_with_right(node *&a)
{
single_rotate_with_left(a->right);
single_rotate_with_right(a);
}
//End of AVL rotations
//Function to return the node. The 'id' variable to be searched is passed as a param
node*& search(int x,node *&t)
{
if(t->id>x)
return search(x,t->left);
else if(t->id<x)
return search(x,t->right);
else if(t->id==x)
{
return t;
}
else
return nullnode;
}
//End of search. I'm using this in the loadnode() function.
//This is where I try to write data back into the file.
void update1(node *&t,int x) // x is the control variable
{
if(x==1)
//This block will be executed only once when the function is called for the
//first time. Used to seek to the beginning of the file
{
file.seekg(0,ios::beg);
x++;
}
if(t!=NULL)// Inorder traversal in the tree
{
update1(t->left,x);
//writing the data in the same order as it was stored.
file<<t->id<<endl;
file<<t->pwd<<endl;
file<<t->name<<endl;
file<<t->add<<endl;
file<<t->city<<endl;
file<<t->pn<<endl;
file<<t->bal<<endl;
update1(t->right,x);
}
}
public:
//Avl Constructor - This one is the one which is actually used.
avl(int x,int p,char nam[15], char a[30], char c[10],int pin,double b)
{
root= new node(x,p,nam,a,c,pin,b,NULL,NULL,-1);
nullnode=new node;
}
avl()
{
root->left=root->right=NULL;
root->height=-1;
}
//Call to the private insert function
void insert1(const int &x,int p,char nam[15], char a[30], char c[10],int pin,double b)
{
insert(x,p,nam,a,c,pin,b,root);
}
//Call to the private print() function
void display()
{
cout<<endl;
print(root);
}
//Function to write a new value for 'bal' variable to a node.
//I'm actually using this to update a node anconfirm whether the value of the updated node
//is reflected back at the node
void loadnode(int x)
{
node *&t=search(x,root);
cout<<"\nLoaded node...\n";
cout<<t->id;
cout<<" "<<t->name;
t->bal=40000;
cout<<"\nUpdated Bal.."<<t->bal;
}
void update()
{
//file.seekp(0);
update1(root,1);
}
};//End of AVL Class
main()
{
cout<<"The output..\n";
int i, p, pn;
char n[15],a[30],c[10];
double b;
int prev_id=0;
file>>i>>p>>n>>a>>c>>pn>>b;
prev_id=i;
avl list(i,p,n,a,c,pn,b);
while(file)
{
file>>i>>p>>n>>a>>c>>pn>>b;
if(prev_id!=i)
// I'm using this because i got a weird scenario in which the last record was repeated twice.
{
list.insert1(i,p,n,a,c,pn,b);
}
prev_id=i;
}
cout<<endl<<"The elements in AVL tree are...\n\n";
list.display();
list.loadnode(12);//12 is the id i used for one of my records.
//Calling to write back the data into the file.
list.update();
file.close();
getch();
return 0;
}
//End of program

Answer 1

If file.good() returned false, some previous operation on the file failed (maybe even a read operation) and raised one of the error flags of the file object. An ugly way to solve it is to use file.clear() which will clear the error flag and allow next actions to execute successfully. A better way to solve it will be to check after each operation if there's an error (file.good() is false) and understand why this operation fails and fix it.

Answer 2

call seekp() to move the write pointer to the begining of the stream (fstream). seekg() moves the get pointer - not going to help when writing...