Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

Construct a signal set and add one signal.

basic_signal_set(
    const executor_type & ex,
    int signal_number_1);

This constructor creates a signal set and registers for one signal.

ex: The I/O executor that the signal set will use, by default, to dispatch handlers for any asynchronous operations performed on the signal set.
signal_number_1: The signal number to be added.

This constructor is equivalent to performing:

boost::asio::signal_set signals(ex);
signals.add(signal_number_1);