Handle std::thread::hardware_concurrency()

Question

In my question about std::thread, I was advised to use std::thread::hardware_concurrency(). I read somewhere (which I can not find it and seems like a

Answer 1

Based on common predefined macros link, kindly provided by Joachim, I did:

int p;
#if __GNUC__ >= 5 || __GNUC_MINOR__ >= 8 // 4.8 for example
  const int P = std::thread::hardware_concurrency();
  p = (trees_no < P) ? trees_no : P;
  std::cout << P << " concurrent threads are supported.\n";
#else
  const int P = my_hardware_concurrency();
  p = (trees_no < P) ? trees_no : P;
  std::cout << P << " concurrent threads are supported.\n";
#endif