Using cin and cout in different threads. Why is the cin buffer removing the first char?

I am trying to make a socket program that lets two people chat. I have one thread for sending a message and another for receiving a message. When I use cin, it cuts off the first char that I input.

I've been looking at different threads here about cin and cout being tied and not being very thread safe, but nothing has worked.

Here is my send and receive threads: RECV

char buffer[32];
  while(true)
  {
    memset(&buffer, 0, sizeof(buffer));
    unsigned long bytes_recv;

    bytes_recv = recv(socketfd, &buffer, sizeof(buffer), 0);

    if(bytes_recv == 0)
    {
      break;
    }

    for(unsigned long i = 0; i < bytes_recv; i++)
    {
      buffer[i] = buffer[i] ^ key;
    }

    printf("Message Received: %s\n", buffer);
  }

and Send

char buffer[32];
  int conn = 1;
  while(true)
  {
    memset(buffer, 0, sizeof(buffer));

    std::cout << "Send a message to host: ";
    std::cin.clear();

    std::cin.getline(buffer, sizeof(buffer));

    std::cout << "StrLen: " << strlen(buffer) << std::endl;

    for(unsigned long i = 0; i < strlen(buffer); i++)
    {
      std::cout << "Char: " << buffer[i] << std::endl;
      buffer[i] = key ^ buffer[i];
    }
    conn = send(socketfd, &buffer, strlen(buffer), 0);
    if(conn == -1)
    {
      break;
    }
  }

If I type "Hello", the buffer only reads "ello" even from the cin thread.