call a string from a method

Cervo2paille

Hello,
I want to call a string from another method :

void ajouterproduit::on_loadPicture_clicked()
{
    QString nameFile = QFileDialog::getOpenFileName(this, tr("Choisir"), "", tr("Images(*.png *.jpg *.jpeg *.gif)"));
}

I tried someting like :

void ajouterproduit::on_pushButton_2_clicked()
{
  QString produit_image = nameFile ;
}

But it doesn't work.
Any idea ?
Thanks

mchinand

@Cervo2paille said in call a string from a method:

The error disappear, but the content of my variable is empty. It's normal, i define it in the function next to it.
And i don't know how to proceeded.

Show us your updated header and ajouterproduit::on_loadPicture_clicked() method. If you have the following in your on_loadPicture_clicked() method (or any other method of ajouterproduit) do you know what the output of each debug statement will be?

   nomFichier = "Hello";
   QString nomFichier = "World";
   qDebug() << "Local value: " << nomFichier;
   qDebug() << "Member value:" << this->nomFichier;

or what it will be in another method if on_loadPicture_clicked() has already been called:

void ajouterproduit::other_method(){
   qDebug() << "nomFichier: " << nomFichier;
}

JonB

@Cervo2paille
Of course it does not work, if namefile is a local variable inside one method how do you expect it to be visible to the outside world?

C++ basics: if you want a method to return a value make it return that value instead of being void.

If it's a slot, like you show, maybe store the chosen filename as a class member (in ajouterproduit) and provide a getter method to return it to the outside world. Or, depending on usage, write a signal with a parameter of the filename which is emitted when the file is chosen so that the outside world can put a slot on that.

Or, since both these methods are inside the same ajouterproduit class, just make nameFile a class variable and the second method will see the value the first method has previously set.

Cervo2paille

Thanks for your precious help.
I'm in the last situation : the two functions are inside the same class.
I tried to to this :
in my .h :

private:
        QString nomFichier;

and in my .cpp

ajouterproduit::ajouterproduit(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::ajouterproduit)
{
    ui->setupUi(this);
    QString nomFichier = QFileDialog::getOpenFileName(this, tr("Choisir"), "", tr("Images(*.png *.jpg *.jpeg *.gif)"));
}

But now my first function doesn't work.
My code can compile but the value of my QString when i click on the button is emp ty "".
Any idea?
Thanks

JonB

@Cervo2paille said in call a string from a method:

Any idea?

Please, nicely, you need to brush up on some C++ basics:

private:
        QString nomFichier;
...
method()
{
   QString nomFichier = ...
}

Is that second QString nomFichier referring to the first one? (Hint: it is not.) It is a quite separate one. What do you have to do to make the second one use the first one?

Cervo2paille

In fact...
This is my question : how can i do it ?
I can define my variable nomFichier at the opening of the QDialog, but the moment when i put the good value to this variable if when i use a clicked() function. Si i'm already in a function...
I don't know how to proceed.

Thanks

JonB

@Cervo2paille
You are asking how to access a class member variable inside the same class in C++. You cannot have got this far without knowing that. Are you asking how to read and set class variables?

Cervo2paille

My problem is simple.
I got a value in this when i click on a button :

void ajouterproduit::on_loadPicture_clicked()
{
    QString nomFichier = QFileDialog::getOpenFileName(this, tr("Choisir"), "", tr("Images(*.png *.jpg *.jpeg *.gif)"));
}

I want to get my nomFichier in another function, which is in the same file, same class :

void ajouterproduit::on_pushButton_2_clicked()
{  /*QString produit_image = nomFichier;*/ }

But my second function doesn't see the first.
No maybe i don't know how to set and get variable in a same class.

The difficulty in that i need to put the value in my function, and if i move it i got a problem : i don't get the value.
Someone can explain me exactly why i'm supposed to do ?

Thanks

Christian Ehrlicher

@Cervo2paille said in call a string from a method:

No maybe i don't know how to set and get variable in a same class.

Ok, then take a step backwards and search for a good c++ beginners book or online tutorial and learn about c++ member variables.

Cervo2paille

Ok thanks.
I found a course and i will try that.
My difficulty is that i create a variable and affect an ACTION in the same line :

    QString nomFichier = QFileDialog::getOpenFileName(this, tr("Choisir"), "", tr("Images(*.png *.jpg *.jpeg *.gif)"));

How can i separate them ? thanks

Christian Ehrlicher

@Cervo2paille said in call a string from a method:

My difficulty is that i create a variable and affect an ACTION in the same line :

No, please learn c++

mchinand

You have what's called a local shadow variable. If you're using QtCreator, it probably even shows you a warning regarding it.

Cervo2paille

My problem is about QT, not C++.
If initialize my QString in my header, this starts the action because it's linked.
To dissociate the creation a my QString :

QString nomFichier

and the affectation that i gave it :

QFileDialog::getOpenFileName(this, tr("Choisir"), "", tr("Images(*.png *.jpg *.jpeg *.gif)"));

The lesson of C++ doesn't help me to do that. And i need to give the access of this action to all my function in the same class.

Thanks

Edit : @mchinand thanks. In fact, i got an error. I can define in my .h this :

    QString nomFichier;

The error disappear, but the content of my variable is empty. It's normal, i define it in the function next to it.
And i don't know how to proceeded.
Define my variable in my .h using the affectation doesn't work : it launch at the started of my Qdialog, and i don't want it. (https://en.wikipedia.org/wiki/Member_variable)
Thanks.

mchinand

@Cervo2paille said in call a string from a method:

The error disappear, but the content of my variable is empty. It's normal, i define it in the function next to it.
And i don't know how to proceeded.

Show us your updated header and ajouterproduit::on_loadPicture_clicked() method. If you have the following in your on_loadPicture_clicked() method (or any other method of ajouterproduit) do you know what the output of each debug statement will be?

   nomFichier = "Hello";
   QString nomFichier = "World";
   qDebug() << "Local value: " << nomFichier;
   qDebug() << "Member value:" << this->nomFichier;

or what it will be in another method if on_loadPicture_clicked() has already been called:

void ajouterproduit::other_method(){
   qDebug() << "nomFichier: " << nomFichier;
}

Cervo2paille

God, Thanks.
I understand what was wrong in what i did...

void ajouterproduit::on_loadPicture_clicked()
{
    nomFichier = QFileDialog::getOpenFileName(this, tr("Choisir"), "", tr("Images(*.png *.jpg *.jpeg *.gif)"));
}

And define for all in my .h the QString.

Thanks again !

SGaist

Hi,

@Cervo2paille said in call a string from a method:

My problem is about QT, not C++.
If initialize my QString in my header, this starts the action because it's linked.

Class member variables declaration, their usage in functions and shadowing them are nothing Qt specific, it's pure C++ knowledge. The fact that yours is used in slots does not change that.

You also likely had warnings from the compiler about the the variable being declared again in a function.

Never ignore compiler warnings, they are bugs waiting to bite you.