Model crashed after static_cast

Ivan Netskin

Hello, let me represent the problem:

I'm populating my model with Item object

class Item{
..........
void installData(Data* ptr);
Data *data();
..........
}

Now suppose this:
1)AdditionalData class is inherited from Data
2)Now in the installData function i've put the initialized AdditionalData pointer;

And now getting the problem:

data(const QModelIndex& index, int role)const{
Item* item=reinterpret_cast<Item*>(index.internalPointer())
Data* itemData=item.data();
AdditionalData* addtionalData=static_cast<AdditionalData*>(itemData);
//IF I CALL ANY METHOD FROM addtionalData THE PROGRAM WILL CRASH otherwise everything is fine
}

Any suggestions? Thanks in advance;

jsulm

@Ivan-Netskin Well, you should ALWAYS check the pointer after casting. And it should be reinterpret_cast, not static_cast.
If itemData is Data and not AdditionalData the cast will fail and you will get a null pointer.

Ivan Netskin

@jsulm
yes, i know, i should. I just wrote it for simplicity. In my code i have just 1 item with initialized AdditionalData so it's for sure Item contains pointer to the AdditionalData object

jsulm

@Ivan-Netskin Why do you use static_cast?
Did you check whether addtionalData is nullptr?

Ivan Netskin

yes i did and it is not, i can get some additional info from the pointer and after that the program will crash. Like i said, if u don't touch the pointer(not calling any of it's member functions) the program will not crash.

Flotisable

@Ivan-Netskin
I think you should check if additionalData is realy a AdditionalData*

Ivan Netskin

Okay, the code was correct!
the line caused the crash :

qDebug()<<model->data(model->index(1,0),Qt::DisplayRole);

because there is only 1 item like i said. Thanks guys anyway!

kshegunov

@jsulm said in Model crashed after static_cast:

And it should be reinterpret_cast, not static_cast.

I think you made a typo here, it must be dynamic_cast.

@Ivan-Netskin said in Model crashed after static_cast:

Okay, the code was correct!

With those reinterpret_casts (here it's necessary, I know, but at least check for NULL) and static_casts you're on a slippery slope ... neither is safe casting, so you may at some point in the future spend some hours debugging them.