C++ 读取文件内容到指定类型的变量

#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;
}