checking for EOF, reading input

[gibran]

Hey everyone i am having a problem with reading input from a text file that looks like this:

9 1 1
1.2 -2.3 0.4
-2 -3 -4
+0 -2 8.85
2.345

The problem is that i am not reading the last line (2.345).

#include <iostream>
#include <fstream>
using namespace std;

int main()
{
double a, b, c;
ifstream input("quadratic.dat");

input>>a>>b>>c;
while (!input.eof())
{
cout<<"a: "<<a<<" b:"<<b<<" c:"<<c<<endl;
input>>a>>b>>c;
}
return 0;
}

Thanks in advance

[ne555]

You are trying to read 3 numbers, but the input just have 1, so you reach the end of file.
¿Could you explain the structure of the file?

[webJose]

Because the last line contains only one number, the line extracting 3 values is failing (probably after a successful extraction for variable a?). This failure may be causing grief. Now, I am no expert with streams in C++, so I'll just tell you what I would do:

1. Never use multiple extraction statements because you never know when one will fail.
2. Read the entire line as a string, and then use a string stream to extract the 3 values. What will happen if you had:

0
12
231 3423 231

??? I imagine that multiple extraction statements would take data from different rows, and the variables would end up like this:

a = 0
b = 12
c = 231

This means that the next a will be 3423, and that the next C will take data from the next line, which could be highly undesirable.

3. Always loop while (stream.good()) and not just by eof(). The fail bit is as important.

[gibran]

I wanted to extract 3 numbers at a time, i.e. 9, 1, 1 first, so i could send those 3 values to function first.

Then Repeat for the second set of numbers, 1.2 -2.3 0.4, send them to the same function

All this in a loop.

So

read form txt file,
cast the 3 values int variables (9,1,1)
send variables to function
return to main
read from txt file again
cast the 3 values int variables (1.2 -2.3 0.4)
send variables to function

[ne555]

¿then why the last line just got 1 number? ¿do you want "default" values for the others?

1. Never use multiple extraction statements because you never know when one will fail.

If it fails, you will know that it failed. However you can't know where it failed, ¿but do you care? If the data is corrupted, ¿what is the best that you can do?
2. I like to input things with spaces, some people use the enter key. You could read both that way.
3. while(input>>a>>b>>c) (if you accept the previous points)