QLabel->setText with access violation

[A Former User]

Hi Community,
I would love to hear what are your assumptions to this error. I tried to overwrite a QLabel's text and I got the following error: "Access violation reading location 0xDDDDDF25".

in my groupBoxWidget.h class there's this member pointer declared as private and a public Setter:

public:
void SetInputMode();
private:
QLabel *m_pLabelTitle1;
//in the Class Constructor it is defined with a empty string:
//m_pLabelTitle1 = new QLabel("");

This method is in the groupBoxWidget.cpp defined as follows:

void CGroupBoxWidget::SetInputMode()
{
	m_pLabelTitle1->setText(tr("Add files with extension:"));
}

First I tried to delete the "translation (tr)" and kept only the raw text between quotemarks. It didn't solve the problem. Then I tried to pass a constant QString by reference as:

const QString test = tr("Add files with extension:");
m_pLabelTitle1->setText(&test);

And it didn't work. But then I deleted the ampersand (&) and it worked! I cannot see what is the error/conflict factor here.

I'm using Qt 5.8 with MSVC v15.

[JonB]

@Arantxa
If you got an "Access violation" you sre supposed to run under a debugger and look at the stack trace when it happens, then you would know where the problem is.

Then I tried to pass a constant QString by reference as:
const QString test = tr("Add files with extension:");
m_pLabelTitle1->setText(&test);

This is not passing something by reference! It is passing it by pointer/address, which is quite different. And QLabel::setText() does not accept a QString * so it won't compile. Standard C++.

First verify that m_pLabelTitle1->setText("Hello") does work. Then so far as I can see there is no reason why setText(tr("Add files with extension:")); would not work if const QString test = tr("Add files with extension:"); m_pLabelTitle1->setText(test); does work. As I say, check in debugger.