How to check that Qwidget exist

Question

Like in title how to check that child class from QWidget exist?

when i try something like that it break application end throw error

void MainWindow::slotAddLoginData() {
    if(!addLoginData) {
        addLoginData = new AddLoginData(this);
        connect(this, SIGNAL(setEnabledALDbtnOK(bool)),
        addLoginData, SLOT(btnOkEnabled(bool)));

    }
    addLoginData->show();
    addLoginData->activateWindow();

}

Unexpected end of program. When i remove "if" statements everything is allright — sebastian, Dec 11 '10 at 21:30
Run it with a debugger (e.g. GDB on \*NIX systems) and tell us *where* it breaks. — Georg Fritzsche, Dec 11 '10 at 21:36
Is it a segmentation fault? My guess is that your parent class isn't initialising addLoginData to NULL. — asdfjklqwer, Dec 11 '10 at 22:00
exactly! setting NULL in the constructor solves the problem, thx :) — sebastian, Dec 11 '10 at 22:03

score 1 · Answer 1 · answered Dec 11 '10 at 22:30

1

It looks like addLoginData is not initialised

answered Dec 11 '10 at 22:30

PiedPiper

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score 1 · Answer 2 · answered Dec 12 '10 at 02:28

1

As others have said, addLoginData isn't initialized. You can't do this:

if(!addLoginData) { ... }

Unless you initialize addLoginData to 0. So, as Georg said, initialize it, except make that..

MainWindow::MainWindow() : addLoginData(0)

(note the "0")

answered Dec 12 '10 at 02:28

OliJG

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`addLoginData()` and `addLoginData(0)` do exactly the same thing here - default initialization means zero initialization in case of scalar types... See e.g. [here](http://stackoverflow.com/questions/936999/what-is-the-default-constructor-for-c-pointer). – Georg Fritzsche Dec 20 '10 at 14:03

score 0 · Answer 3 · answered Dec 11 '10 at 21:14

0

One possibility would be that you have not initialized addLoginData. Use something like this in that case:

MainWindow::MainWindow()
  : addLoginData()
  // ...
{
    // ...
}

answered Dec 11 '10 at 21:14

Georg Fritzsche

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How to check that Qwidget exist

3 Answers3