How to extract a custom object from QVariant?

[BeefTaco]

I'm using low level pcap library, to get interfaces, and put them inside combo box, with the associated name, so user can select, which to use. I use qvariant constructor QVariant(int typeId, const void * copy)

 pcap_if * devs = GetDevices();
 for(auto d = devs; d != nullptr; d = d->next){
        this->ui->comboInterfaces->addItem(d->description, QVariant(0,d));
    }

But how can i extract the pcap_if * pointer to object from qvariant?

I try like that:

Q_DECLARE_METATYPE(pcap_if *);
pcap_if * test = data.value<pcap_if*>();

test is null. How can i extract my pointer? Help

[Gojir4]

Hello,

You can try to put Q_DECLARE_METATYPE(pcap_if *); after the class declaration.

class pcap_if 
{
public:
    pcap_if ()
    {
    }
};    
Q_DECLARE_METATYPE(pcap_if *)

And you have to use QVariant::setValue() or QVariant::fromValue() to set the pointer value correctly:

  pcap_if * devs = GetDevices();
  for(auto d = devs; d != nullptr; d = d->next){
    this->ui->comboInterfaces->addItem(d->description, QVariant::fromValue(d));
    //or 
    //QVariant v;
    //v.setValue(d);
    //this->ui->comboInterfaces->addItem(d->description, v);
  }

edit: Another point, I didn't find any QVariant's constructor with two arguments, what did you try to achieve with QVariant(0, d) ? I did find it finally :)

See this post: https://stackoverflow.com/questions/44501171/qvariant-with-custom-class-pointer-does-not-return-same-address

[BeefTaco]

But pcap_if _t* is not my class it is a low level struct defined inside pcap library from pcap.h:

/*
 * Item in a list of interfaces.
 */
struct pcap_if {
	struct pcap_if *next;
	char *name;		/* name to hand to "pcap_open_live()" */
	char *description;	/* textual description of interface, or NULL */
	struct pcap_addr *addresses;
	bpf_u_int32 flags;	/* PCAP_IF_ interface flags */
};

. But from what you respond iguess i can wrap it inside some class.

[Gojir4]

@BeefTaco Ok, I think you can put it in the main, or at some place in your code where it is executed before you use it with a QVariant.

[Gojir4]

As an alternative, you could also cast it to a void *, as suggested by the second reply on the stackoverflow's post I referred.