Segmentation Fault through signal SIGSEGV



  • Alright, this is something new to me. After googling around I found out that segmentation faults are given when the program is pointed to use memory that it doesn't have access to.

    I've recently started experiencing these errors after I tried making a custom button class that would enclose, in its clicked() signal, an integer.

    Here's the custom button class:
    .h:
    @#include <QtGui>

    #ifndef CUSTOMBUTTON_H
    #define CUSTOMBUTTON_H

    class CustomButton : public QPushButton //This simple class allows us to map arguments in the Widget's cicked() signal.
    { //In the project, it's used in the delete-edit buttons so the program knows which part of the Movie/Theater/Screening list we're referring to
    Q_OBJECT

    public:
    CustomButton(QString name,int num, QWidget *parent = 0);

    signals:
    void clicked(int pos);

    private:
    QSignalMapper *signalMapper;
    };

    #endif // CUSTOMBUTTON_H@

    .cpp:
    @#include "custombutton.h"

    CustomButton::CustomButton(QString name,int num = 0, QWidget *parent) //Our constructor
    : QPushButton(name,parent)
    { //Our button's now created and shown, through the superconstructor. Let's take care of its clicked() signal.

    signalMapper = new QSignalMapper(this);
    
    connect(this, SIGNAL(clicked()), signalMapper, SLOT(map()));
    signalMapper->setMapping(this, num);
    
    
    connect(signalMapper, SIGNAL(mapped(int)),this, SIGNAL(clicked(int)));
    

    }@

    And then in my main code I do:
    @CustomButton *edit_button = new CustomButton("Edit",i,0);
    edit_button->setFixedWidth(30);
    connect(edit_button,SIGNAL(clicked(int)),this,SLOT(edit_movie(int))); //When the user decides to edit a movie, we set the class'es working_with var to the position of the film in the MovieList and we set the screen to the appropriate one.

    CustomButton *del_button = new CustomButton("Delete",i,0); //We pass i as an argument to the button, so it can relate to the movie it's set next to.
    del_button->setFixedWidth(45);
    connect(del_button,SIGNAL(clicked(int)),this,SLOT(del_movie(int)));@

    Where i is the number I want it to have in the signal.

    Thing is, thorugh the debugger it doesn't give me a segfault if I press the Delete button. It all happens in the edit one.

    As I'm still pretty confused and in a situation where I don't even know WHAT to ask about, if you need anything else from me please say so and I will provide.

    Here's the backtrace:

    0 QHash<QObject*, QString>::findNode qhash.h 884 0x69e98594
    1 QHash<QObject*, QString>::contains qhash.h 874 0x69e98568
    2 QSignalMapper::map qsignalmapper.cpp 267 0x69debe0c
    3 QSignalMapper::map qsignalmapper.cpp 257 0x69debda2
    4 QSignalMapper::qt_static_metacall moc_qsignalmapper.cpp 64 0x69debfce
    5 QMetaObject::activate qobject.cpp 3547 0x69de9baf
    6 QAbstractButton::clicked moc_qabstractbutton.cpp 220 0x10cb4b8
    7 QAbstractButtonPrivate::emitClicked qabstractbutton.cpp 548 0xe2e517
    8 QAbstractButtonPrivate::click qabstractbutton.cpp 541 0xe2e495
    9 QAbstractButton::mouseReleaseEvent qabstractbutton.cpp 1123 0xe2f941
    10 QWidget::event qwidget.cpp 8362 0xae63de
    11 QAbstractButton::event qabstractbutton.cpp 1082 0xe2f7cc
    12 QPushButton::event qpushbutton.cpp 683 0xecfeba
    13 QApplicationPrivate::notify_helper qapplication.cpp 4554 0xa9c020
    14 QApplication::notify qapplication.cpp 4097 0xa9a26a
    15 QCoreApplication::notifyInternal qcoreapplication.cpp 876 0x69dd3b76
    16 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 234 0x113137e
    17 QApplicationPrivate::sendMouseEvent qapplication.cpp 3163 0xa98ad6
    18 QETWidget::translateMouseEvent qapplication_win.cpp 3363 0xb03171
    19 QtWndProc qapplication_win.cpp 1696 0xafdf66
    20 USER32!IsDialogMessageW C:\Windows\syswow64\user32.dll 0 0x76726238
    21 USER32!RegisterSystemThread C:\Windows\syswow64\user32.dll 0 0x767278b0
    22 ?? 0 0x30000
    23 USER32!AllowForegroundActivation C:\Windows\syswow64\user32.dll 0 0x767268ea
    24 qt_is_translatable_mouse_event qapplication_win.cpp 1463 0xafd465
    25 USER32!GetMessageExtraInfo C:\Windows\syswow64\user32.dll 0 0x76727d31
    26 ?? 0

    And here is what



  • Let me also note that if I don't run the program through the debugger, it sporadically crashes.

    Most of the time clicking the Edit button will take me where I want to be with no problem.
    Sometimes it crashes.



  • Why use a heavy weighted object like the signal mapper here? A much more simple approach would be to use a small protected slot that emits your signal:

    @

    class CustomButton : public QPushButton
    {
    Q_OBJECT

    public:
    CustomButton(QString name,int num, QWidget *parent = 0);

    signals:
    void clicked(int pos);

    private slots:
    void emitClickedWithInt();

    private:
    int myNumber;
    };

    CustomButton::CustomButton(QString name,int num, QWidget *parent)
    : QPushButton(name, parent), myNumber(num)
    {
    connect(this, SIGNAL(clicked()), this, SLOT(emitClickedWithInt()));
    }

    void CustomButton::emitClickedWithInt()
    {
    emit clicked(myNumber);
    }
    @


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