Add a signal to a signal_set.

void add(
    int signal_number);
  » more...

void add(
    int signal_number,
    asio::error_code & ec);
  » more...

Add a signal to a signal_set with the specified flags.

void add(
    int signal_number,
    flags_t f);
  » more...

void add(
    int signal_number,
    flags_t f,
    asio::error_code & ec);
  » more...