QObject::connect crashing

  • I have a simple class that inherits from QWidget and am using the Q_OBJECT macro in my class defnition. I am compiling the header file using moc and including the generated cpp file in my class definition cpp. In the contructor of my class I am attempting to connect a signal from a button to a slot defined in my class. During runtime I am seeing a crash in the connect call and it appears that the metadata for the generated class contains a bunch of NULLs which are the source of the crash as they are dereferenced down in the connect call.

    I have used the moc compiler many times on other projects, so I must be missing something either in the command line for moc or some setup prior to the connect calls. Any ideas?

  • can you provide any source code?
    Otherwise it's hard to help.

  • Is the button already created at the time you are connecting to it?

  • I will post code when I get home from work, but the button should be constructed in the setupUi routine which is called before the connect.

  • Okay here is the code:

    header file for moc file generation

    #pragma once

    #include <QDockWidget>

    namespace Ui {
    class EditToolWidget;

    class EditToolImpl : public QObject
    EditToolImpl(QDockWidget& parent);

    public slots:
    void colorToolButtonClicked();

    Ui::EditToolWidget *m_ui;

    cpp file that initializes the UI and connects the one slot

    #include "EditToolImpl.h"
    #include <QColorDialog>
    #include "generated\ui_editToolDockWidget.h"

    EditToolImpl::EditToolImpl(QDockWidget& parent)
    m_ui = new Ui::EditToolWidget();
    QObject::connect(m_ui->colorToolButton, SIGNAL(clicked()), this, SLOT(colorToolButtonClicked()));


    void EditToolImpl::colorToolButtonClicked() {
    QColor color;
    color = QColorDialog::getColor(Qt::green, m_ui->dockWidgetContents, QString("Select Color"), QColorDialog::DontUseNativeDialog);

    The command to compile the header file:

    $(SolutionDir)\ThirdParty\Qt\4.8.0\bin\moc.exe -DUNICODE -DWIN32 -DQT_LARGEFILE_SUPPORT -DQT_DLL -DQT_GUI_LIB -DQT_CORE_LIB -DQT_HAVE_MMX -DQT_HAVE_3DNOW -DQT_HAVE_SSE -DQT_HAVE_MMXEXT -DQT_HAVE_SSE2 -DQT_THREAD_SUPPORT -I"$(SolutionDir)\ThirdParty\Qt\4.8.0\include\QtCore" -I"$(SolutionDir)\ThirdParty\Qt\4.8.0\include\QtGui" -I"$(SolutionDir)\ThirdParty\Qt\4.8.0\include" -I"$(SolutionDir)\ThirdParty\Qt\4.8.0\include\ActiveQt" -I"." -I"$(SolutionDir)\ThirdParty\Qt\4.8.0\mkspecs\win32-msvc2010" -D_MSC_VER=1600 -DWIN32 EditToolImpl.h -o generated\moc_EditToolImpl.cpp

    Generated moc_EditToolImpl.cpp

    ** Meta object code from reading C++ file 'EditToolImpl.h'
    ** Created: Tue Feb 7 19:19:52 2012
    ** by: The Qt Meta Object Compiler version 63 (Qt 4.8.0)
    ** WARNING! All changes made in this file will be lost!

    #include "../EditToolImpl.h"
    #if !defined(Q_MOC_OUTPUT_REVISION)
    #error "The header file 'EditToolImpl.h' doesn't include <QObject>."
    #elif Q_MOC_OUTPUT_REVISION != 63
    #error "This file was generated using the moc from 4.8.0. It"
    #error "cannot be used with the include files from this version of Qt."
    #error "(The moc has changed too much.)"

    static const uint qt_meta_data_EditToolImpl[] = {

    // content:
    6, // revision
    0, // classname
    0, 0, // classinfo
    1, 14, // methods
    0, 0, // properties
    0, 0, // enums/sets
    0, 0, // constructors
    0, // flags
    0, // signalCount

    // slots: signature, parameters, type, tag, flags
    14, 13, 13, 13, 0x0a,

       0        // eod


    static const char qt_meta_stringdata_EditToolImpl[] = {

    void EditToolImpl::qt_static_metacall(QObject *_o, QMetaObject::Call _c, int _id, void **_a)
    if (_c == QMetaObject::InvokeMetaMethod) {
    EditToolImpl *_t = static_cast<EditToolImpl *>(_o);
    switch (_id) {
    case 0: _t->colorToolButtonClicked(); break;
    default: ;

    const QMetaObjectExtraData EditToolImpl::staticMetaObjectExtraData = {
    0, qt_static_metacall

    const QMetaObject EditToolImpl::staticMetaObject = {
    { &QObject::staticMetaObject, qt_meta_stringdata_EditToolImpl,
    qt_meta_data_EditToolImpl, &staticMetaObjectExtraData }

    const QMetaObject &EditToolImpl::getStaticMetaObject() { return staticMetaObject; }

    const QMetaObject *EditToolImpl::metaObject() const
    return QObject::d_ptr->metaObject ? QObject::d_ptr->metaObject : &staticMetaObject;

    void EditToolImpl::qt_metacast(const char _clname)
    if (!_clname) return 0;
    if (!strcmp(_clname, qt_meta_stringdata_EditToolImpl))
    return static_cast<void
    >(const_cast< EditToolImpl
    return QObject::qt_metacast(_clname);

    int EditToolImpl::qt_metacall(QMetaObject::Call _c, int _id, void **_a)
    _id = QObject::qt_metacall(_c, _id, _a);
    if (_id < 0)
    return _id;
    if (_c == QMetaObject::InvokeMetaMethod) {
    if (_id < 1)
    qt_static_metacall(this, _c, _id, _a);
    _id -= 1;
    return _id;

    The crash occurs within the connect call indicating that the call to *EditToolImpl::metaObject() is returning NULL data.

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