CODEWITHSUNDEEP
c++
James C
James C

Reputation: 919

I get a SIGSEGV, Segmentation fault, when I try to write to wxListBox ( C++, wxWidgets, CodeBlocks )

The program I am writing can build and get executed from CodeBlocks IDE, but pressing a specific button ( invoking a handler function ) makes program crash. In debugger mode I get this message :

Program received signal SIGSEGV, Segmentation fault.

And it happens in the line :

m_listboxSorted->SetString(k, "some text");


Minimal version of my program, that I hope includes all the important parts of code, is :

class MainFrame: public wxFrame
{
public:    
wxListBox *m_listboxSorted;    
};

bool TestApp::OnInit()
{
MainFrame* OurMainFrame = new MainFrame(constructor info... );
OurMainFrame->Show( true );
return true;
}


MainFrame::MainFrame(constructor info...)
{
wxListBox * m_listboxSorted = new wxListBox(constructor info...);
}

void MainFrame::ButtonClicked(wxCommandEvent & event)
{

    static unsigned int k = 0 ;
    k++;
    m_listboxSorted->SetString(k, "some text"); // !! Problematic line !!
}


Now, after searching online for solution to the signal SIGSEGV, Segmentation fault I figured that the problem must be in the pointer, and dereferencing it. But as a beginner, I was unsuccessful in applying this information to solve my program issue.

EDIT :
I have also tried to change this line : 

wxListBox *m_listboxSorted;

with this one:

wxListBox *m_listboxSorted = new wxListBox;

But this time, when pressing the button ( invoking the handler function ), I get this message :

Error Message

What to correct in my code to make the program function properly ?

Upvotes: 0

Views: 137

Answers (1)

eerorika
eerorika

Reputation: 238311

The member wxListBox *m_listboxSorted; is uninitialized.

wxListBox * m_listboxSorted = new wxListBox(constructor info...);

in the constructor does not assign a value to the member, but instead declares a local pointer which is leaked when the constructor returns.

m_listboxSorted->SetString(k, "some text");

then dereferences the uninitialized member pointer resulting in undefined behaviour.

To fix, remove the type from the line in constructor so that it becomes an assignment rather than a declaration.

Upvotes: 2

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