18 Language support library [language.support]

18.8 Exception handling [support.exception]

18.8.5 uncaught_exceptions [uncaught.exceptions]

int uncaught_exceptions() noexcept;

Returns: The number of uncaught exceptions ([except.uncaught]).

Remarks: When uncaught_exceptions() > 0, throwing an exception can result in a call of
std::terminate() ([except.terminate]).