Accessing value of vector only once

MEsc

Hello, I have a Question.

For example:
void loadfrom() loads values from file into a vector

I have another function MainWindow::on_start_clicked()
When this Function get called (here via button),
values should load in vec.

QVector<QString> vec = loadfrom();

And in another function
MainWindow::on_answer_returned()
At the moment everytime this function get called the vector loads all values everytime. But I want access the vector in this function from MainWindow::on_start_clicked()

How can I do this?

ChrisW67

@MEsc said in Accessing value of vector only once:

I have another function MainWindow::on_start_clicked()
When this Function get called (here via button),
values should load in vec.
QVector<QString> vec = loadfrom();

That looks like vec is a variable local to the slot attached to the button. You load it and then it is destroyed when the slot exits. If you want the vec object to have a longer lifetime then you need to arrange that. As @Christian-Ehrlicher says, making vec a private member variable of the MainWindow class is probably the right approach. So,

class MainWindow: public QMainWindow {
...
private:
  QVector<QString> m_vec
};

void MainWindow::on_start_clicked() {
...
  m_vec = loadfrom();
...
}

void MainWindow::on_answer_returned() {
...
  // do stuff with m_vec
...
}

This is basic C++ knowledge and not Qt specific.

Christian Ehrlicher

@MEsc said in Accessing value of vector only once:

How can I do this?

Do not load it again when it's already loaded I would guess. Maybe by storing it in a member variable?

ChrisW67

@MEsc said in Accessing value of vector only once:

I have another function MainWindow::on_start_clicked()
When this Function get called (here via button),
values should load in vec.
QVector<QString> vec = loadfrom();

That looks like vec is a variable local to the slot attached to the button. You load it and then it is destroyed when the slot exits. If you want the vec object to have a longer lifetime then you need to arrange that. As @Christian-Ehrlicher says, making vec a private member variable of the MainWindow class is probably the right approach. So,

class MainWindow: public QMainWindow {
...
private:
  QVector<QString> m_vec
};

void MainWindow::on_start_clicked() {
...
  m_vec = loadfrom();
...
}

void MainWindow::on_answer_returned() {
...
  // do stuff with m_vec
...
}

This is basic C++ knowledge and not Qt specific.