C++ – How to detect empty lines while reading from istream object in C++

c++inputistreamstreamstring

How can I detect if a line is empty?

I have:

1
2
3
4

5

I'm reading this with istream r
so:

int n;
r >> n

I want to know when I reach the space between 4 and 5.
I tried reading as char and using .peek() to detect \n but this detects the \n that goes after number 1 . The translation of the above input is: 1\n2\n3\n4\n\n5\n if I'm correct…

Since I'm going to manipulate the ints I rather read them as ints than using getline and then converting to int…

Best Solution

It could look like this:

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

int main()
{
    istringstream is("1\n2\n3\n4\n\n5\n");
    string s;
    while (getline(is, s))
    {
        if (s.empty())
        {
            cout << "Empty line." << endl;
        }
        else
        {
            istringstream tmp(s);
            int n;
            tmp >> n;
            cout << n << ' ';
        }
    }
    cout << "Done." << endl;
    return 0;
}

output:

1 2 3 4 Empty line.
5 Done.

Hope this helps.