Virtual pure function call without constructor

Marcel Mueller

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Aug 28, 2022, 12:59:09 PM8/28/22

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Is there *any* scenario how this error can happen without any
constructor or destructor in the call stack?

Marcel

Richard Damon

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Aug 28, 2022, 1:13:07 PM8/28/22

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I can see it happening with threads (the constructor/destructor is in a
different Thread).

Not sure if there is any way to create or slice an object to result in
an "abstract" object.

Paavo Helde

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Aug 28, 2022, 1:37:39 PM8/28/22

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28.08.2022 19:58 Marcel Mueller kirjutas:
> Is there *any* scenario how this error can happen without any
> constructor or destructor in the call stack?

Sure, when you call via an invalid pointer where the object has been
already destroyed.

Juha Nieminen

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Aug 29, 2022, 7:21:05 AM8/29/22

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Marcel Mueller <news.5...@spamgourmet.org> wrote:
> Is there *any* scenario how this error can happen without any
> constructor or destructor in the call stack?

Is this question different from just asking "is it possible that a member
function is called for an object that has not been constructed?"

I assume that since you mention pure virtuality in particular, you are
thinking of some other scenario here.

Marcel Mueller

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Aug 29, 2022, 9:45:04 AM8/29/22

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Am 28.08.22 um 19:12 schrieb Richard Damon:

> On 8/28/22 12:58 PM, Marcel Mueller wrote:
>> Is there *any* scenario how this error can happen without any
>> constructor or destructor in the call stack?

> I can see it happening with threads (the constructor/destructor is in a
> different Thread).

That's UB. Anything can happen.

> Not sure if there is any way to create or slice an object to result in
> an "abstract" object.

The compiler should prevent that kind of slicing because no variable of
an abstract type can exist.

Marcel

Marcel Mueller

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Aug 29, 2022, 9:56:24 AM8/29/22

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Am 28.08.22 um 19:37 schrieb Paavo Helde:

Hmm.

It turned out that I accidentally called a constructor in
std::vector<>::emplace_back(...) rather than just passing constructor
arguments. Once I removed this unnecessary temporary object the error
(later in the application) was gone.

It was a small number crunching application that did neither use any
multi-threading nor new/delete (except for std::vector internally) and
all class variables are POD or one of the classes of POD's or a
reference to it.
The latter was likely the problem. The automatically generated move or
copy constructor probably somehow generated a dangling reference.

Marcel

Manfred

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Aug 29, 2022, 8:29:16 PM8/29/22

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If you have virtual functions, then it's not a POD.

Richard Damon

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Aug 30, 2022, 7:50:03 AM8/30/22

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On 8/29/22 9:44 AM, Marcel Mueller wrote:
> Am 28.08.22 um 19:12 schrieb Richard Damon:
>> On 8/28/22 12:58 PM, Marcel Mueller wrote:
>>> Is there *any* scenario how this error can happen without any
>>> constructor or destructor in the call stack?
>
>> I can see it happening with threads (the constructor/destructor is in
>> a different Thread).
>
> That's UB. Anything can happen.

Yep, and the error mentioned is one of them.

>
>> Not sure if there is any way to create or slice an object to result in
>> an "abstract" object.
>
> The compiler should prevent that kind of slicing because no variable of
> an abstract type can exist.
>
>
> Marcel

That's why I said "Not Sure". I wasn't going to say definitively that it
wasn't possible.

The comment about accessing the distructed object was one way to get
such a sliced object (but again, invoking Undefined Behavior).