#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;}