C++ reads file contents to a variable method of the specified type

As shown below:

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
 
using namespace std;
 
int main(){
	cout << "input the file name: ";
	string file_name;
	cin >> file_name;
	cout << endl;
 
	// ifstream infile("1.txt");
	ifstream infile(file_name.c_str());
	string line;
	while (std::getline(infile, line)){
		std::istringstream iss(line);
		int a, b;
		if (!(iss >> a >> b)) { break; } // error
		cout << "a : " << a << endl;
		cout << "b : " << b << endl;
	}
	return 1;
}