[SOLVED] Read file line by line using ifstream in C++

Read file line by line using ifstream in C++

The contents of file.txt are:

Where 5 3 is a coordinate pair. How do I process this data line by line in C++?

I am able to get the first line, but how do I get the next line of the file?

ifstream myfile;
myfile.open ("file.txt");

Solution

First, make an ifstream:

#include <fstream>
std::ifstream infile("thefile.txt");

The two standard methods are:

Assume that every line consists of two numbers and read token by token:
```
int a, b;
while (infile >> a >> b)
{
    // process pair (a,b)
}
```

Line-based parsing, using string streams:

#include <sstream>
#include <string>

std::string line;
while (std::getline(infile, line))
{
    std::istringstream iss(line);
    int a, b;
    if (!(iss >> a >> b)) { break; } // error

    // process pair (a,b)
}

You shouldn't mix (1) and (2), since the token-based parsing doesn't gobble up newlines, so you may end up with spurious empty lines if you use getline() after token-based extraction got you to the end of a line already.