QList pointer function to abstract class

Question

I feel dumb for asking this question because it seems like it would be simple but I don't know how to do it and I can't find it anywhere on the internet. I'm trying to make a function that will return a QList to standard output, the pointer to the abstract class is confusing me. The AbstractStudent class generates an instance of another class Student. here is the function:

QList<AbstractStudent*>* StudentList::returnList() const{


}

So what's the problem/question? Right now you are returning a pointer to a `QList` that holds base class pointers. I can't see why do you need to return a _pointer_ to the `QList`, but it still works. — SingerOfTheFall, Sep 20 '13 at 06:48
to send the list to standard output so it can be printed in a QTextEdit — Dmon, Sep 20 '13 at 06:59

score 1 · Accepted Answer · answered Sep 20 '13 at 07:12

A list which stores pointers of an abstract class will be able to store pointers to any sub class of that abstract class.

Think of the following:

AbstractStudent.h:

class AbstractStudent 
{
    // ...
};

Student.h:

class Student : public AbstractStudent
{
    // ...
};

Any other class .cpp:

QList< AbstractStudent* > studentList;

// Each of the following works:
AbstractStudent* student1 = new Student( /* ... */ );
studentList.append( student1 );

Student* student2 = new Student( /* ... */ );
studentList.append( student2 );

Student* student3 = new Student( /* ... */ );
AbstractStudent* student3_1 = student3;
studentList.append( student3 );

I am however a bit confused of your last sentence, claiming that AbstractStudent generates Student objects. I would have expected that Student inherits AbstractStudent and some other class generates Student objects, like in my example.

AbstractStudent is the base class for the concrete Student class. StudentList is implemented as a list of pointers to AbstractStudent instances - the list will then contain pointers that point to instances of concrete student instances. StudentList is implemented with the Singleton design pattern. (It's like Inception for programming :D). Thanks that helps — Dmon, Sep 20 '13 at 07:26
Alright. It first sounded like AbstractStudent would have `new Student()` somewhere in its code, so I was confused. ;-) Before you get all too fancy about singletons though, I recommend reading: http://stackoverflow.com/questions/137975/what-is-so-bad-about-singletons and http://misko.hevery.com/2008/08/17/singletons-are-pathological-liars/ — Tim Meyer, Sep 20 '13 at 09:23

QList pointer function to abstract class

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