Explain terminate() and unexpected() function

terminate() is a library function which by default aborts the program
It is called whenever the exception handling mechanism cannot find a handler for a thrown exception.

unexpected() is called when a function with an exception specification throws an exception of a type that is not listed in the exception specification for the function
A function declaration without a specification like throw(char*) may throw any type of exception, and one with throw() is not allowed to throw exceptions at all.

By default unexpected() calls terminate().