How to group values from the same line into a pair? - c++

Question

I am trying to write a program that reads a text file which has a data set in the form below and puts every 2 integers per line into a pair:
1 2
3 4
5 6
... and so on
Currently, this part of my main code reads the file line by line and converts the imported strings to integers one number at a time, but I am not sure how I would group 2 integers at a time in each line and put them in a pair. Ultimately, I want to add all the pairs to a single set.
while (getline(fs, line)) {
istringstream is(line);
while(is >> line) {
int j = atoi(line.c_str());
cout << "j = " << j << endl;}}

Answer 1

You could simply use std::pair, like this:
istringstream is(line);
pair<int, int> p;
is >> p.first;
is >> p.second;
cout << p.first << " " << p.second;
In next step you could use std::set<std::pair<int, int> > to acheive your goal of putting the pairs into single set.

Answer 2

Try this:
std::ifstream ifs{ "yourfile.txt" };
// read line by line
std::string line;
while(std::getline(ifs, line)) {
std::istringstream iss{ line }; // make a stream on the line
auto values = std::make_pair<int, int>(0, 0);
if(iss >> values.first >> values.second) { // check stream state
// after reading two ints
// (this skips spaces)
std::cout << "a=" << values.first << ", b=" << values.second << "\n";
} else {
throw std::runtime_error{ "bad data" };
}
// at this point, you have read a valid pair of ints into "values"
}
See the code comments for explanations.

Answer 3

Use pair available in 'utility' header, following is the sample code for the same.
while (getline(fs, line))
{
stringstream is;
is<<test;
int i, j;
is>>i;
is>>j;
pair<int, int> pr(i,j);
}

Answer 4

Following may help:
std::string line;
std::set<std::pair<int, int>> myset;
while (std::getline(fs, line)) {
std::istringstream is(line);
int a, b;
if (is >> a >> b) {
myset.insert({a, b});
} else {
throw std::runtime_error("invalid data");
}
}
Live example
To consider 1, 5 as identical as 5, 1, you may use:
struct unordered_pair_comp
{
bool operator () (const std::pair<int, int>& lhs, const std::pair<int, int>& rhs) const
{
return std::minmax(lhs.first, lhs.second) < std::minmax(rhs.first, rhs.second);
}
};
and so your myset becomes std::set<std::pair<int, int>, unordered_pair_comp> myset;
Live example

Answer 5

Something like this should work for your purposes.
while (getline(fs, line))
{
istringstream is(line);
int i, j;
is >> i >> j;
std::pair<int,int> my_pair = std::make_pair (i, j);
}

Answer 6

Dont make the imported strings into integers. Read the two strings from one line and concatenate them. Then make them integers. Like this:
#include <sstream>
#include <fstream>
#include <string>
#include <iostream>
using namespace std;
int main()
{
string line;
ifstream fs("input.txt");
while (getline(fs, line))
{
istringstream is(line);
string num1, num2;
while (is >> num1 >> num2)
{
num1 += num2;
int j = stoi(num1);
cout << "j = " << j << endl;
}
cin.get();
}
}