Overwriting of a text file.

[spacer15]

It is a function to overwrite the value of an account. Basically it creates a temporary file, copies all the accounts except the one which we are working on to the temporary file. At the end it writes the account which we were working on. And at the end it just copies all the contents of the temp file to the account.txt file again. So that the value of the account is over written. But the account.txt file is coming out empty. Help please.
Forgive me for the unusual way of coding.

  void write(){
		
		           string temp2;
                   int temp;
		           ofstream tempfile ("temp.txt");
		           ifstream mainfile  ("Accounts.txt");
		
		           do{
			
                      mainfile >> temp;
		              if(temp != Accno){
			
                      tempfile << temp<< " ";
		
		              for(int a=0; a<4; a++){
		
			                  mainfile >> temp2;
			                  tempfile << temp2 << " ";	
	                    }			
                       tempfile << endl;
		               }
		               else{
			
			                for(int a=0; a<4; a++)
		                    	mainfile >> temp2;
			
		                     }
		
    }while(!mainfile.eof());
	
	
	tempfile << Accno << " "
		<< PIN	<< " "
		<< Amount << " "
		<< Fname << " "
		<< Lname<< endl;
		
	
	
	mainfile.close();
	tempfile.close();
	
	tempfile.open("Accounts.txt");
	mainfile.open("temp.txt");
	
	
	for (int a=1; !mainfile.eof(); a++){
		mainfile >> temp2;
		if(mainfile.eof()) break;
		tempfile << temp2 << " ";
		if (a%5==0)
		tempfile << endl;
		
	}
	
	tempfile.close();
	mainfile.close();
}

[Duthomhas]

I don't see why the file should come out empty. I get:

D:\prog\foo>type Accounts.txt
1 1234 12.34 One Eleven
2 2341 23.41 Two Twelve
3 3412 34.12 Three Thirteen
4 4123 41.23 Four Fourteen

D:\prog\foo>a
Accno> 2
PIN> 7
Amount> 76.54
Fname> Seven
Lname> Twelves

D:\prog\foo>type Accounts.txt
1 1234 12.34 One Eleven
3 3412 34.12 Three Thirteen
4 4123 41.23 Four Fourteen
4 Fourteen Fourteen Fourteen Fourteen
2 7 76.54 Seven Twelves

D:\prog\foo>

There are a number of serious flaws, though... (sorry).


1) Don't loop on EOF.
That's where the list of fourteens is coming from. Your loop would work better to fail after trying to read an Accno:

while (mainfile >> temp) {
  if (temp != Accno) {
    ...

You actually get it right on line 49: Attempt to read, break from loop if failed to read. (This is why you don't see more duplication madness.)

2) Global variables
Accno, PIN, etc, are all global variables. Shouldn't you have those in a struct somewhere? One you can pass as argument to your function?


3) Non-descriptive or misleading names
The write() function doesn't just write stuff.
There is no obvious difference between mainfile and tempfile (though "tempfile" is an okay name).


4) Don't re-use streams.
It works okay here, but it'll bite you at some point.


5) Structural problem
This carries from the previous points.
You would do better to load the entire file into memory (into an array or a deque or something), modify it there, then rewrite the file. That's two or three functions each.

struct account {
  int Accno;
  int PIN;
  ...
};

void load( string filename, vector<account>& accounts ) {
   ifstream f( filename.c_str() );
   account acct;
   while (f >> acct.Accno) {
     f >> acct.PIN;
     ...
     accounts.push_back( acct );
   }
}

void save( string filename, vector <account>& accounts ) {
  ofstream f( filename.c_str() );
  ...
}

int main()
{
  vector<account> accts;

  load( "Accounts.txt", accts );

  account acct = get_account_information_from_user();
  int accno = -1;

  // find the account to change, if any
  for (int x = 0; x < accts.size(); x++)
    if (accts[ x ].Accno == acct.Accno)
      {
      accno = x;
      break;
      }

  // add the new account or change the existing account
  if (accno < 0)
  {
    accts.push_back( acct );
  }
  else
  {
    accts[ accno ] = acct;
  }

  save( "Accounts.txt", accts );
}

Hope this helps.

[spacer15]

I actually really like your idea but the thing is i need to submit this project in the next 6 hours. And im really kinda busy implementing the interface of this program. It's a program of an ATM.

I managed to get the file running but the error you stated, the fourteen fourteen fourteen one is now happening to me if i open another account. If you could correct this error for me in this file that would be so great.

[Duthomhas]

See (1) for the problem with that.