//
// Linux: compile using
//    g++ -std=c++17 threads_printer.cpp -pthread
//
#include <iostream>       
#include <chrono>
#include <thread>
#include <mutex>
#include <string>
#include <fstream>
#include <vector>

namespace demo{
  class Printer{
  private:
    std::mutex printmtx_;    
  public:
    void print(std::string file, int x) {
      std::lock_guard<std::mutex> lock(printmtx_);  
      std::cout << "thread id "<<std::this_thread::get_id() << " printing to file " << file << '\n';
      std::ofstream out(file);
      out<<x<<"\n";
      out.close();
    }
  };
}

int main() {
  demo::Printer printer;
  auto job = [&printer](int x){printer.print("test",x);};
  std::vector<std::thread> ths;
  
  for(int i=0;  i<10; i++){
    std::thread th(job,i);
    ths.push_back(std::move(th)); // must use std::move
  }
  for(auto &th: ths) th.join();  // must use auto &
}