reading data fom files

Hi

If I have a data file with numbers that I want to store in an array. What C++ finction can I use?

ie.

Data_file

# velocity
3
4.5
6.1
-3
...N

and i want to store these in array x[N]

Code:

---


int main(){

double x[N];

}

---

Thanks

Shuo

Code:

---

int main(){

        double x[N];

        ifstream in("file.txt");

        int i = 0;
        while (i < N && in >> x[i])
        {
                i++;
        }
}

---

what headers do i need for ifstream?

I included

#include <fstream>
#include <iostream>

Don't forget

Code:

---

using namespace std;

---

or

Code:

---

std::ifstream

---

For ifstream, the header fstream is required.

How do I skip variable headers in the data file like

Velocity
.5
4
,,,

Density
1.2
0.3
...

Do you mean how do you skip certain lines?

yes, I want to store them in arrays a[] and b[].

One way is to use getline() to skip a line:

Code:

---

#include <string>
.
.
std::string line;
getline(in, line);

---

what about mutiple lines do i have to repeat the getline() each time?
Thanks

Yes. The function reads one line at a time.

Is there a way of skipping a defined number of lines?

The easiest way is just reading a specified number of lines. Otherwise you can seek in the file, but it's by position, not lines, so it's not very efficient, since you have to manually check for line ends and count and stuff.
There's no function to do what you want, at least none that I know of.