[Interest] QSharedpointer members are not accessible: isNull and data

[Giuseppe D'Angelo]

Hi,

On 23/10/2020 14:16, Tamás Nagy wrote:
> class A
> {
> public:
> ....
> private:
>      QSharedPointer<QValidator> m_Validator;
> }
> 
> My custom program:
> 
>   if(di.Validator()->isNull())
>   {
>              // unfortunately the di.Validator() is null
>              // some A-s in the Map can have nullptr as Validator.
> 
>              if(auto validator = di.Validator())   // di is an instance of A
>              {
>                  if(validator != nullptr)
>                  {

I'm having quite a hard time understanding this code.

In the first if, you dereference the result of di.Validator(). This 
implies it's not null.

Then immediately after you fetch di.Validator() again, assign it to 
"validator", and in the second if you ask if it's not null -- but... you 
already know?.

Then in the third if you ask *again*. What's going on here?

Can you put together a minimal but complete, correct, and compileable 
testcase?

Thanks,
-- 
Giuseppe D'Angelo | giuseppe.dangelo at kdab.com | Senior Software Engineer
KDAB (France) S.A.S., a KDAB Group company
Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com
KDAB - The Qt, C++ and OpenGL Experts

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