WxWidgets Sizer Double Frees?

Question

I'm going to preface this question by saying that I am not entirely new to wxWidgets, though I would not consider myself all that experience either.

I'm having a problem which I have narrowed down through testing to be with the wxWidgets wxBoxSizer classes. From what I can tell, I don't think I'm doing anything wrong, and they work while the application is running; however, when the application closes and everything terminates, it seems that about a third of the time it will double-free something and seg fault. I'm writing and building on a linux system, and there doesn't seem to be any problems with anything but these sizers.

I did have many more windows within the HomeFrame class before I stripped it to search for bugs, but the code below still causes the double-free:

I've also looked around StackOverflow and other code forums to see if anyone was having a similar issue, but I couldn't find anything. I'm thinking that it may have something to do with the way I'm storing the sizer pointers in the class as members?

HomeFrame.h:

#pragma once

#include <wx/frame.h>
#include <wx/sizer.h>

namespace qzrgui
{
    class HomeFrame: public wxFrame
    {
    public:
        HomeFrame();
        ~HomeFrame();

    private:
    //  Sizers

        wxBoxSizer* _topSizer;
        wxBoxSizer* _leftSizer;
        wxBoxSizer* _rightSizer;

    //  Functions

        void _setup();
        void _createWindows();
    };
}

HomeFrame.cpp:

#include "HomeFrame.h"

namespace qzrgui
{
    HomeFrame::HomeFrame() :
    wxFrame(nullptr, wxID_ANY, "Quizzer")
    {
        _setup();
    }
    
    HomeFrame::~HomeFrame() 
    {
        
    }
    
    void HomeFrame::_createWindows() 
    {
    //  Create sizers.

        _topSizer = new wxBoxSizer(wxOrientation::wxHORIZONTAL);
        _leftSizer = new wxBoxSizer(wxOrientation::wxVERTICAL);
        _rightSizer = new wxBoxSizer(wxOrientation::wxVERTICAL);
    }
    
    void HomeFrame::_setup() 
    {
        _createWindows();
    }

}

Quizzer.h (wxApp base class):

#pragma once

#include <wx/app.h>


namespace qzrgui
{
    class Quizzer : public wxApp
    {
    public:
        virtual bool OnInit();
    };
};

Quizzer.cpp:

#include "Quizzer.h"

wxIMPLEMENT_APP(qzrgui::Quizzer);

#include "frames/HomeFrame.h"

namespace qzrgui
{
    bool Quizzer::OnInit()
    {
        wxFrame* frame = new HomeFrame();
        frame->Show(true);

        return true;
    }
}

do you need to store the sizers as members? Also, which wx version do you use and under which platform? — Igor
Your class violates the rule of 3/5/0: https://en.cppreference.com/w/cpp/language/rule_of_three — drescherjm
I assume you have a delete somewhere in code you are not showing. — drescherjm
@Igor I guess I don't need to, but I was doing so for organizational purposes while I was building the class. I didn't think it would change anything. I'm using wxWidgets 3.1.4 on Ubuntu Linux. — Andrew Huffman
@drescherjm I know, this class is just for demonstration purposes. I had the destructor defined because I was messing around with termination stuff in it to see if I could wrap my head around what's going on. — Andrew Huffman

VZ. VZ. · Accepted Answer · 2020-09-15T20:52:23

There is nothing in the code shown here which could result in a crash. You do definitely have (three) memory leak(s) in your code, as you create 3 sizers not associated with any window or another sizer and never delete them, but, while wrong, this can't result in a crash.

There is also not enough information to diagnose what you're seeing. As always with a crash, please build your code with debug information and run it under debugger to see what exactly happens. If you're under a Unix-like system (or even under MSW with the latest MSVS 2019 version), you should also compile with address sanitizer enabled to find the real problem before the crash happens.

WxWidgets Sizer Double Frees?

1 Answers