Question

I have a rather simple C++-problem, but coming from a C-background I am not really aware of all the I/O capabilities of C++. So here is the problem:

I have a simple .txt file with a specific format, the textfile looks like this:

123 points are stored in this file
pointer number | x-coordinate | y-coordinate
0      1.123      3.456
1      2.345      4.566
.....

I want to read out the coordinates. How can I do this?
The first step is fine with:

int lines;
ifstream file("input.txt");
file >> lines;

This stores the first number in the file (i.e. the 123 in the example) in lines. Now I’d like to iterate over the file and only read the x and y coordinates. How can I do this efficently?

Answer 1

I’d probably do it just about like I would in C, just using iostreams:

std::ifstream file("input.txt");

std::string ignore;
int ignore2;
int lines;
double x, y;

file >> lines;
std::getline(ignore, file);   // ignore the rest of the first line
std::getline(ignore, file);   // ignore the second line

for (int i=0; i<lines; i++) {
     file >> ignore2 >> x >> y;    // read in data, ignoring the point number
     std::cout << "(" << x << "," << y << ")\n";   // show the coordinates.
}