TCP Server in C/C++: Send timeout message

I was looking for a way to set timeout for one connection and I've already found some very good answers, but timeout alone isn't enough for me.

I want my last server -> client message to be an announcement about timeout. I don't want to suddenly interrupt connection with client leaving them clueless.

What I'm looking for:

if ( /* should timeout now */ )
{
   char timeout_msg [] = "Connection timed out";
   if (send(sock_fd,  timeout_msg, sizeof(timeout_msg), 0) < 0)
   {
      perror("Sending problem");
      return whatever;
   }

   //actually time out now
}