How can you get the Linux thread Id of a std::thread()

Question

I was playing with std::thread and I was wondering how is it possible to get the thread id of a new std::thread(), I am not talking about std::t

Answer 1

How about this:

pid_t gettid (void)
{
    return syscall(__NR_gettid);
}

http://yusufonlinux.blogspot.com/2010/11/get-thread-id-from-linux.html

Looks like __NR_gettid is defined in unistd.h