Advice about the application I will be making? (I'm a beginner)

[dvlpr.bernard]

@mrjj Hello, no. I mean the QString ch_topic whenever the user chooses a topic. How I'm going to get the ch_topic in order to use it in other functions?

[mrjj]

@dvlpr.bernard
Hi
Just store in main window class.
All the data you want to be shared between functions should be part of MainWindow. (in .h)
At least stuff like selected Topic etc.

[dvlpr.bernard]

@mrjj
Hello, Hmm didn't know why this is happening. What I did wrong?

[mrjj]

Hi
You say get_ch_topic is of type MainWindow ???
Should it not QString ?
Or do you mean it should be a function to return
the ch_topic ?
In any case, type of MainWindow just seems wrong.

[dvlpr.bernard]

@mrjj
I don't know. But I want to define a global object so that other functions can use it. But I just don't know where to declare it

[mrjj]

@dvlpr.bernard
Hi
Just like the
QString ch_topic;
Then all member functions have access to it as they are part of the class.

[dvlpr.bernard]

@mrjj
whenever I use qDebug() <<get_ch_Topic.getTopic() in the same function where ch_topic was define it returns "IF". But when I use qDebug() <<get_ch_Topic.getTopic() in other functions it return "". I don't know why but maybe because the object name was different?

[mrjj]

Hi
Do NOT make new instances of the main window class like you do

that is just plain wrong.

You are already in an instance. So no need to ever make new ones.
you can simply use the ch_topic variable.
Its already declared in the MainWindow you are using already.

[dvlpr.bernard]

@mrjj
Sir, that's what I did before but whenever I do that it says

[mrjj]

well
just use the variable directly. no need to use function.
im not sure what get_ch_tipic is as you dont have () so its not function call.

However, if you do

QString MyX; ( in .h as you shown)

then anywhere you can just use it like

MyX = "";
or read it.

is just bad syntax.
as you say get_ch_Topic is a object with the function getTopic and its not true.

if you gave MainWindow a function called getTopic
then just call it
qDebug() << getTopic();

Its important to understand that all you add to MainWindow class ( in .h)
can be access from any functio that also a memebr .
that is
MainWindow::SomeFunction() {
any variable from .h you can use here. no special syntax. just use it.
}

[dvlpr.bernard]

Thank you sir. I just don't know but still it doesn't work it just return "" not "WHILE". :(

[mrjj]

@dvlpr.bernard
hi
check code where you set it.
Maybe you create other instance you set it on ?

[dvlpr.bernard]

@mrjj
Hello sir,
Where should I declare a global instance / object in my 3 files.
mainwindow.h, main.cpp, or mainwindow.cpp?
Ang how whenever I declare one because whenever I declare one e.g. (MainWindow get_ch_Topic;) it display an error "no previous extern declaration for non-static variable"

[jsulm]

@dvlpr.bernard said in Advice about the application I will be making? (I'm a beginner):

Where should I declare a global instance / object in my 3 files.

Nowhere! Avoid global variables especially if those are derived from QObject!
Why do you need global variables at all?

[dvlpr.bernard]

This post is deleted!

[dvlpr.bernard]

@jsulm
Hello sir. So that I can access the string that I declared in other functions.
How could I do it the right way?

0_1556355591803_f0274585-e5f9-4e11-8428-9341f8853a75-image.png

[mrjj]

Hi
Put all the variables in the class!

class MainWindow : public QMainWindow
{
Q_OBJECT

public:
explicit MainWindow(QWidget *parent = nullptr);
~MainWindow();
...
private:
Ui::MainWindow *ui;
QString ch_Dif_Lvl; ///// HERE !
QString fc_Topic;
};

then you can just use them

void MainWindow::on_pushButton_clicked()
{
    ch_Dif_Lvl = "BEGINNER";
   fc_Topic = "Topic";
}

[dvlpr.bernard]

@mrjj
Thank you. God bless your kindness to help other people.

[mrjj]

@dvlpr.bernard
Thank you :)
I hope the project is progressing fine.

[dvlpr.bernard]

@mrjj
Good day sir.

I have been trying to get the data from my database it is already connected but whenever the query executes qDebug() returns "QSqlQuery::exec: database not open".

Also I tried to replace this query
qry.exec("select Question from mydatabase where QQuantity = 4 and Topic = 'FOR' and Difficulty_Level = 'ADVANCED'")
with variable and string name
qry.exec("select Question from mydatabase where QQuantity = '"+quantity+"'and Topic = '"ch_topic"' and Difficulty_Level = '"ch_dif_lvl"'")
but it didn't work also.