A signal handler must meet the requirements for a handler. A value h of a signal handler class should work correctly in the expression h(ec, n), where ec is an lvalue of type const error_code and n is an lvalue of type const int.

Examples

A free function as a signal handler:

void signal_handler(
    const asio::error_code& ec,
    int signal_number)
{
  ...
}

A signal handler function object:

struct signal_handler
{
  ...
  void operator()(
      const asio::error_code& ec,
      int signal_number)
  {
    ...
  }
  ...
};

A lambda as a signal handler:

my_signal_set.async_wait(
    [](const asio::error_code& ec,
      int signal_number)
    {
      ...
    });

A non-static class member function adapted to a signal handler using std::bind():

void my_class::signal_handler(
    const asio::error_code& ec,
    int signal_number)
{
  ...
}
...
my_signal_set.async_wait(
    std::bind(&my_class::signal_handler,
      this, std::placeholders::_1,
      std::placeholders::_2));

A non-static class member function adapted to a signal handler using boost::bind():

void my_class::signal_handler(
    const asio::error_code& ec,
    int signal_number)
{
  ...
}
...
my_signal_set.async_wait(
    boost::bind(&my_class::signal_handler,
      this, asio::placeholders::error,
      asio::placeholders::signal_number));