Qt retrieving reference out of a struct inside a QList-CodePudding

i have a struct "Material" which has a referencetype of Item& Item is a baseclass for many different Materials who can appear in a list. The struct also has an integer variable and also a QString variable. Those two are just give the amount to be used and a String of what type item must be casted back.

struct Material
{
    int amount;
    Item& item;
    QString itemtype;
    Material(int myamount,Item& myitem,QString myitemtype) : amount(myamount),item(myitem),itemtype(myitemtype){}
};

As i have read here: initialize struct contain references to structs

to have a reference sitting inside of a struct one need to define a constructor within the struct. as you can see in the upper Material struct.

Now when i try to retrive the reference of that, like here:

QList<Material> Mats = bp.Materials();
for(int i=0;i<Mats.count();i  )
{
      Item& item = Mats[i].item;
}

i allways get an error like "use of deleted function 'Material& Material::operator=(const Material&)"

I also tried already to define such a operator= but obviously if i try to return the rvalue which is const i can't do this because the lvalue is not const. and if i make a new instance of Material it is going to be an implicit copy constructor.

My Question: What do i miss here?

On the wish to make a reproduceable example, i may got to the problem. I have no solution for my one just yet but an idea what may have caused this:

#include <QCoreApplication>
#include <QList>

struct Kram
{
   QString& text;
   Kram(QString& s): text(s) {}
};



int main(int argc, char *argv[])
{
   QCoreApplication a(argc, argv);

   QString mytext= "Hello, World!";
   Kram k(mytext);

   QList<Kram> liste;
   liste.append(k);

   for(int i=0; i<liste.count();i  )
   {
      QString& anothertext = liste[i].text;
   }

return a.exec();

}

When i compile this he tells me the exact same error message about the "Kram" struct. But this only appears if you do the struct in a Qlist and then try to get the reference inside of the struct out.

just to mention the second error message is in both cases thisone:

C:\Users\Rolf\Documents\Testprojekt\main.cpp:4: Fehler: non-static reference member 'QString& Kram::text', can't use default assignment operator

CodePudding user response：

For all who stumble on this, i will post my fixed example code. But i highly recommend to read the comments from Scheff's Cat and sigma below my question. Because they give you some really important infos why this is happening. I my self will consider the idea of sigma to use the std::unique_ptr for my code.

eyeball in the following code that now the struct holds a pointer but the constructer gets a reference so that there is no nullpointer. but still the object here in the main code can be assigned normaly meaning no pointer involved there.

here is the code:

#include <QCoreApplication>
#include <QList>

struct Kram
{
   QString* text;
   Kram(QString& s): text(&s) {}
};



int main(int argc, char *argv[])
{
   QCoreApplication a(argc, argv);

   QString mytext= "Hello, World!";
   Kram k(mytext);

   QList<Kram> liste;
   liste.append(k);

   for(int i=0; i<liste.count();i  )
   {
      QString* anothertext = liste[i].text;
   }

   return a.exec();
}

thank you all for helping me finding out of this maze