14 Exception handling [except]

14.6 Special functions [except.special]

14.6.3 The std​::​uncaught_exceptions function [except.uncaught]

An exception is considered uncaught after completing the initialization of the exception object until completing the activation of a handler for the exception ([except.handle]).
[Note 1: 
As a consequence, an exception is considered uncaught during any stack unwinding resulting from it being thrown.
— end note]
If an exception is rethrown ([expr.throw], [propagation]), it is considered uncaught from the point of rethrow until the rethrown exception is caught.
The function std​::​uncaught_exceptions ([uncaught.exceptions]) returns the number of uncaught exceptions in the current thread.