iostream vs fstream

gen_data.rb

(1..1000000).each do
  puts "12345"
end

test1.cpp

#include <ctime>
#include <iostream>
#include <vector>

using namespace std;
int main(){
  vector<int> data;
  int input;

  while (cin >> input)
  {
        data.push_back(input);
  }
  cout << "Data loaded." << endl;
}

test2.cpp

#include <ctime>
#include <iostream>
#include <fstream>
#include <vector>

using namespace std;
int main(int argc, char *argv[]){
  vector<int> data;
  int input;
  ifstream in;
  cout << argv[1];
  in.open(argv[1]);

  while (in >> input)
  {
        data.push_back(input);
  }
  cout << "Data loaded." << endl;
}