Cannot use QStringList defined in header file

[mono]

Hi,
I am very new to Qt, I've only done a few small apps so I'm sorry if this is a silly question.
I wanted to make a small library of items from a videogame I play. I created a class "Item" in the "item.h" file and as you can see the item has 3 attributes (name, price, description). My idea was to create list for each of them, so I could then push back the values in the list each time the "Item" constructor is called. The reason I want to do that is so that I could later use these lists to pass is as an argument to QCompleter and other widgets. But for some reason whenever i call the list in my "mainwindow.cpp" file, it gives an error of "undefined variable" or "invalid use to non-static member". I've tried adding the prefix "Item::", it stopped the error but it didn't display anything in the widget that I passed it to. The header is included in the file and it is also included in the .pro file, so I am confused as to where I'm making a mistake. Thanks for any help, the code is bellow

item.h

#ifndef ITEM_H
#define ITEM_H
#include<QString>
#include<QStringList>

class Item{ 
public:
    QStringList l_name;
    QStringList l_description;
    QStringList l_price;

    QString name;
    QString description;
    int price;

    Item(QString n, int p, QString d)
    {
        name = n;
        description = d;
        price = p;
        saveItem();
    }

    void saveItem()
    {
        l_name.append(name);
        l_description.append(description);
        l_price.append(QString::number(price));
    }

};

#endif // ITEM_H

mainwindow.cpp

#include "window.h"
#include "item.h"
//#include "item.cpp"

Item ammo_scav("Ammo Scav", 500, "description of item");
Item extra_charge("Extra Charge", 500, "Description of item");

window::window(QWidget *parent)
    : QWidget{parent}
{
    setFixedSize(700, 700);
    lbl_name = new QLabel(l_name[0], this);
}

If I change to this, it works perfectly fine

lbl_name = new QLabel(ammo_scav.name, this);

[JonB]

@mono
l_name is a member variable of class Item.
lbl_name = new QLabel(l_name[0], this); is inside window::window(), a constructor for some window class.
The two classes have nothing to do with one another (so far as C++ is concerned), you can't access a variable in one from the other. Hence the "undefined variable" on l_name.
If you had an instance of Item you might access item.l_name or item->l_name, but that's another matter.
ammo_scav.name works because you have a global variable (probably not a good idea in itself) ammo_scav (of class Item) which is visible to window::window().

You need to have a fair working knowledge of C++ to write Qt applications with it, Qt also offers a binding for Python which some people find easier than C++. Both of them require an understanding of classes and instances.

[mono]

@JonB I am kind of learning C++ as I progress with my Qt knowledge. So sometimes I find myself unaware of some basic knowledge, thank you for telling me

[Pl45m4]

@mono said in Cannot use QStringList defined in header file:

I am kind of learning C++ as I progress with my Qt knowledge

You should learn Qt as your C++ knowledge progresses, not the other way :)
Solid C++ fundamentals are essential to enjoy working with Qt.
You see what happens when you struggle with C++ basics ;-)