Can std::cout set badbit or failbit with the operator <<? If so, when?

Question

Can std::cout set the badbit or failbit with the operator <<. If so, when does this occur?

Answer 1

std::cout maps to lower-level OS facilities, and anything that could make the OS fail its write will show up as failbit or badbit. For example, on Linux, you can cause this to happen by closing stdout:

int main(int argc, char* argv[])
{
  close(1);
  std::cout << "Hello, world!" << std::endl;
  return cout.fail(); // returns 1
}

(And, because file descriptors are inherited, your calling process may have closed stdout for you.)