Catch block for exception thrown in a destructor

Question

I have some "nested" try catch blocks, split across functions, but essentially it boils down, for classes Foo and Bar, to this:

try { for (;;){ try { Foo foo; try { Bar bar; if (something){ continue; } } catch (...){ std::cout << "inner"; } } catch (...){ std::cout << "middle"; } } } catch (...){ std::cout << "outer"; }

Both classes can throw exceptions in their destructors.

If continue is reached then as the stack unwinds, and during the destruction of foo and bar, an exception is thrown, then I'm expecting to print "outer", but it doesn't do that. What is going on?

why would it print something? where are you throwing an exception? — David Haim
– David Haim, Commented Jul 6, 2015 at 13:00
@DavidHaim as it says "Both classes can throw exceptions in their destructors". — davmac
– davmac, Commented Jul 6, 2015 at 13:07
you don't throw an exception from a destructor. see stroustrup.com/bs_faq2.html#ctor-exceptions — David Haim
– David Haim, Commented Jul 6, 2015 at 13:08
Unfortunately I use a 3rd party base class that does. So needed to know which catch site the exception will go to. — P45 Imminent
– P45 Imminent, Commented Jul 6, 2015 at 13:11
"If continue is reached then as the stack unwinds, and during the destruction of foo and bar, an exception is thrown" - this shows some confusion somewhere. The stack doesn't unwind until an exception is thrown. "continue" being reached has nothing to do with stack unwinding. — davmac
– davmac, Commented Jul 6, 2015 at 13:11

Bathsheba · Accepted Answer · 2015-07-06 13:02:55Z

The standard makes this clear:

If a destructor throws an exception then it is caught by the try block in which the variable is defined.

So if ~Bar() throws an exception, then the output is "inner". If ~Foo() throws, then the output is "middle";

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