Example for https://essential-cpp.programming-books.io/stdatomic-ede1fd1200134e8ba92d109c2ef39c10 (made with https://codeeval.dev)

main.cc

#include <iostream>       // std::cout
#include <atomic>         // std::atomic, std::memory_order_relaxed
#include <thread>         // std::thread

std::atomic_int foo (0);

void set_foo(int x) {
  foo.store(x);     // set value atomically
}

void print_foo() {
  int x;
  do {
    x = foo.load();  // get value atomically
  } while (x==0);
  std::cout << "foo: " << x << '\n';
}

int main ()
{
  std::thread first (print_foo);
  std::thread second (set_foo,10);
  first.join();
  second.join();
  return 0;
}