Re: subclassing std::exception, where to store what() error string?
On Dec 2, 4:45 am, Fedor Rodikov <rodikov.fe...@gmail.com> wrote:
On Nov 29, 1:33 am, Joshua Maurice <joshuamaur...@gmail.com> wrote:
I think that throwing from exception's constructor is OK, because no
exception is being handled at the time you construct the exception
object. Sure, you see e.g. "throw xyz(params)", but that's actually
xyz::xyz unnamed_exception_object(params);
throw unnamed_exception_object;
... where throw was preceded by another, so it's as if it was never
reached.
Is there any legalese on that? Honest question.
I'm pretty sure your interpretation is correct. Before the exception
constructor exits, the throw statement has not "fully evaluated", so
no exception is pending, so if you throw from the exception
constructor, you're fine. At least, I'd be highly surprised if it went
any other way.
Hi!
If an exception is thrown during a copy-construction of any exception
object then a program can be terminated.
The copy of exception object can be made after throw statement
(internally) or in catch statement.
I think this example isn't safe.
I think I was correct but not clear enough, and you are more correct.
Consider:
struct Foo { Foo() { throw 1; } };
int main()
{
try
{
throw Foo();
}
catch (int& )
{
return 1;
}
catch (Foo& )
{
return 2;
}
return 0;
}
In that code, it has perfectly defined behavior. It's going to return
1. That's all I was trying to say.
You did correctly note the FAQ.
http://www.parashift.com/c++-faq-lite/exceptions.html#faq-17.17
So, it's possible that during exception handling of the OP's example,
a bad_alloc will be thrown, and the program will die. At least, that's
how I understand it.
Before, exception handling was allowed to copy the exception object
any number of times. I'm wonder if C++11 has changed the rules to
require using move construction over copy construction if available in
this case. Because if so, then you won't get bad_alloc thrown as the
OP's exception is move-able.