You can make a std::thread run in the background by calling std::thread::detach() on it.

• Once detached, a thread continues to run in the background and cannot be communicated with or waited upon to complete.
• When you detach a thread, the ownership and control passes over to the C++ Runtime Library, which ensures that the resources allocated to the thread are deallocated once the thread exits.

#include <iostream>
#include <string>
#include <thread>
#include <functional>
 
void Count()
{
  for (int i=0; i<100; i++)
  {
    std::cout << "counter at: " << i << std::endl;
  }
}
 
int main()
{
  std::thread t1(Count);
  std::this_thread::sleep_for(std::chrono::milliseconds(10));
  t1.detach();
  return 0;
}