exception raised in destructor

[puzzlecracker]

Allegedly, it is a well-known practice to avoid throwing an exception
from destructor. What are they - consequences and what a general
techniques when exception are possible (like fail to close db
connection or socket, etc)? BTW, how can you have two active exception
at the same time? What is the neteffect; program termination? Does
standard say anything in this regard?

Thanks

 

[Victor Bazarov]

Allegedly, it is a well-known practice to avoid throwing an exception
from destructor.

Why "allegedly"?

What are they - consequences and what a general
techniques when exception are possible (like fail to close db
connection or socket, etc)?

Program termination.

BTW, how can you have two active exception
at the same time?

I can't.

What is the neteffect; program termination? Does
standard say anything in this regard?

Yes, it does. See [except.terminate]/1, the third bullet point.

V

 

[puzzlecracker]

I can't.

Is it not possible, even in theory, to have two or more active
exceptions simultaneously? I read somewhere - in effective c++ or
exceptional c++, don't remember exactly - where an author listed
circumstances where it was possible.


Thanks

 

[Victor Bazarov]

Is it not possible, even in theory, to have two or more active
exceptions simultaneously? I read somewhere - in effective c++ or
exceptional c++, don't remember exactly - where an author listed
circumstances where it was possible.

OK, it's possible. If any destructor during execution of its code
encounters any exception, it better catch it itself. At the time
between throwing such exception and catching it in the destructor
itself, there will be two exceptions "active" simultaneously. Here
is a contrived example:

void foo() throw(int) {
static int a = 42;
throw a++;
}

#include <iostream>

struct A {
~A() {
try {
foo();
}
catch (int i) {
std::cout << "caught " << i << " in ~A()\n";
}
}
};

int main() {
try {
A a;
foo();
}
catch (int i) {
std::cout << "caught " << i << " in main()\n";
}
}


V