Why there is error in assigning values to QString

Question

I want to access the Qstring (m_IPAdd) from a Dialog Window to Main Window. However, I am stuck in passing a Qstring value in a setter function.

My error appears as a pop-up window when debug mode:

unhandled exception occurs at 0x66a77448 (Qt5Cored.dll) in __.exe:0xC0000005: 
conflict happend when accessing the memory at 0xffffffffffffffff"

(I am using MSVC2010 with Qt5.0. )

Dialog Window:

private:
MainWindow *mainwindow;

...

mainwindow->setIPAdd(m_IPAdd);     //m_IPAdd: member variable of class DialogWindow

MainWindow:

private:    
QString m_ip;

...

void MainWindow::setIPAdd(const QString ip)
{
    m_ip = ip ;
}

I also tried

void MainWindow::setIPAdd(const QString ip)
{
    QString ipadd = ip;        //ipadd: local variable which it can get the value of Qstring (in Debug mode) 
    m_ip = ipadd ;             //here's the program crashes, m_ip can't get any value
}

I am wondering why the local variable ipadd can get the value passed through argument ip, but not m_ip. I have even tried assigning

m_ip = "abc";

but the program also fails.

I have read through docs in qt web, but still don't know which part is useful to me.

Please give me any guides and advice. Thank you very much!!

Answer 1

As Dialog Window inherits from QWidget, it is a widget itself. So... you can just define your own Q_PROPERTY on it to represent the value you want to share, and register that property. With that it will be accesible from your mainwindow.