Thread: file reading error

hello,
i am trying to read from a file until EOF, and print details to the screen.
it seems to print extra stuff at the end.
below is my code

Code:

list<Things*> i;
ifstream x ("file.txt");

while(!x.eof())
{
     Things* temp = new Things;
     x.getline(one);
     x >> two;
     x >> three;
     temp->set_one(one);
     temp->set_two(two);
     temp->set_three(three);
     i.push_back(temp);
}

ostream& Foo::printAll(ostream& stream) {
  list<Things*>::iterator a;

    for(a = i.begin(); a != i.end(); ++a)
        stream << (**a).print_details(stream) << endl;

  return stream;
}

ostream& Bar::print_details(ostream& stream) {
        stream  << "ONe: "        << get_one()           << endl
                << "Two: "             << get_two()        << endl
                << "Three: "           << get_three()      << endl
                << endl;
        return stream;
}

and the printout that i actually get when i run my prog is (without the hashes)..
###################
One: eeny
Two: meeny
Three: miny

0x804d1bc
One:
Two: meeny
Three: miny

0x804d1bc
###################

and my file contains (without the hashes)
###################
eeny
meeny miny
###################


can anyone see why its printing it twice and those funny address values aswell?

try a++ instead of ++a

try a++ instead of ++a

this did not work

also, try no print_details instead of stream << print_details

ok this stopped the printing of address's,
it is still printing an extra copy ..like so


One: eeny
Two: meeny
Three: miny

One:
Two: meeny
Three: miny

.........???............seems to me like you don't need the for loop either......
try without it...if that doesn't work post the rest of your code

what are you trying to do with (**a) ?

well i would think i would need the for loop since i want to print out all the nodes in my list. even tho now it only has one, later on i do wish to insert more.

your code doesn't really make sense to me to begin with.....

you have a list containing type Things....yet, inside Bar:rint_details() you reference get_one(), get_two() and get_three() as if they were of type Bar.....is this an inherited class?

I think the problem is here:

Code:

while(!x.eof())
{
	 Things* temp = new Things;
	 x.getline(one);
	 x >> two;
	 x >> three;

eof() as a conditional will often cause an "extra" item to be read in. I'm not very good at explaining it, so I recommend you go here:

http://faq.cprogramming.com/cgi-bin/...&id=1043284351

That reference talks about feof() but the argument holds for eof() as well, as eof() is basically feof() updated for C++ and input streams rather than FILE pointers for C.

As I understand it, when your code calls x >> three, it terminates input when it sees EOF but it doesn't set EOF indicator yet, so when you go back to the start of the while loop, eof() checks to see if EOF indicator is set. It isn't so eof() still returns false, !x.eof() is still true, and the loop body goes on to try to read some more. The behaviour of getline() and >> is undefined at this point since we have gone beyond the end of the file, and the compiler puts whatever it wants into one, two, and three. It often just doesn't do anything so whatever was in one, two, and three remain there, though you can't count on that. Whatever happens to one, two, and three, the code continues and prints out whatever is in one, two and three, and you end up with an extra set of stuff printed out that you hadn't intended.

To fix this I'd try changing the conditional to

while(x.getline(one))

and droppint the call to getline() within the body of the while loop.