Member class in c++

Hello , I am really new in C++ development .
I am working on Qt Application .
I need to call a member class in another class without creating an instance .
Can I do this ?
thank you
There is no such thing as "calling a class". If you mean calling a member function within a class that is defined within another class, okay, but if you want to do it "without creating an instance" then the member function must be static.
The only class members that can be used without an instance are those that are static.

What are you trying to do?
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class MainWindow : public QMainWindow
{
    Q_OBJECT
public:
    Backend *back;


what i want to do is to get back instance in another class without create a new instance of Mainwindow.
Can I do this please
If the other class has a function that returns a MainWindow reference (MainWindow&), sure.

Maybe if you explained what the other object is, how it contains or references a MainWindow object, and what you want to do with this object, we would be better able to help you.
@doug4
Currently I haven't class which return a reference .

what i have actually :
In Mainwindow :
1/ I have a quickwidget which integrate a qml file .
2/ I create a backend instance to get data from it and fill the QMl File
=> So in MainWindow I have a Backend instance
In Backend
1/I have the definition of my data (getter, setter, change slots).

In UploadCSV
1/I have a button when it's clicked a slot in Backend will change some data .
2/After change data I would like to display it on QML .
=> And in UploadCSV I have another Backend instance

=> the problem is when i create 2 instance I can't get data changed .(and it's logic)
this UploadCSV code:
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Backend *back = new Backend(); // this line cause problem 
    connect(ui->parambtn_2, SIGNAL(clicked()),back , SLOT(status()),Qt::QueuedConnection); I must replace back by  th instance created in Mainwindow


I hope is that clear for you
thank you
Rather than explain your code, it would be easier for us if you simply post your code.
thank you all I solve the issue :D :)
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