"Undebuggable" segmentation fault
-
Partially fixed:
QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*->png)"));Now I can open and close the file dialog, but if I select a file the segmentation fault happens here:
this->_line->setText(filename);it seems it doesn't like "this". But I don't know why.
Furthermore if I place a breakpoint there, it will stops, but the debugger shows no information about variables. -
Hi
Its looks ok.
however, every place you do
SignatureEditor *widget = static_cast<SignatureEditor *>(editor);
should make a check if is not null.
before using it.the error/crash you get looks like being inside invalid object. ( not liking this ptr etc )
so i would start check each cast.
SignatureEditor *widget = static_cast<SignatureEditor *>(editor); if (widget) { widget->setText(value); widget->activate(); } else qDebug() << "invalid cast for editor"; -
Hi
Its looks ok.
however, every place you do
SignatureEditor *widget = static_cast<SignatureEditor *>(editor);
should make a check if is not null.
before using it.the error/crash you get looks like being inside invalid object. ( not liking this ptr etc )
so i would start check each cast.
SignatureEditor *widget = static_cast<SignatureEditor *>(editor); if (widget) { widget->setText(value); widget->activate(); } else qDebug() << "invalid cast for editor"; -
@mrjj said in "Undebuggable" segmentation fault:
so i would start check each cast.
They return a non-zero pointer (i.e. no debug message is shown). And the address is the same among the creation of the editor and the two casts.
-
@Mark81
Hi
ok, so seems not that.
Could you try with a completely normal slot and not a lambda ? -
@mrjj said in "Undebuggable" segmentation fault:
Could you try with a completely normal slot and not a lambda ?
Ahah, you read my mind. I've already done that with the same results.
Is really so difficult to do what I'm trying to achieve?@Mark81
hi
Hmm. out of ideas then.
No, it seems very ok to have a custom widget and open a file dialog.so if it crashes at
this->_line->setText(filename);
its either "this" or _line that is not ok and we need to find out why.
i assume
this->_line->setText("test");
with no dialog also crashes ? -
@Mark81
hi
Hmm. out of ideas then.
No, it seems very ok to have a custom widget and open a file dialog.so if it crashes at
this->_line->setText(filename);
its either "this" or _line that is not ok and we need to find out why.
i assume
this->_line->setText("test");
with no dialog also crashes ?@mrjj said in "Undebuggable" segmentation fault:
i assume
this->_line->setText("test");
with no dialog also crashes ?Instead this works!
BUT:this also works:
connect(_btn, &QToolButton::clicked, [this]() { QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)")); });while this crashes:
connect(_btn, &QToolButton::clicked, [this]() { QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)")); this->_line->setText("test"); }); -
Hi
butconnect(_btn, &QToolButton::clicked, [this]() { this->_line->setText("test"); });does not crash? so it does seems to be dialog related ?
-
Hi
butconnect(_btn, &QToolButton::clicked, [this]() { this->_line->setText("test"); });does not crash? so it does seems to be dialog related ?
-
@mrjj said in "Undebuggable" segmentation fault:
i assume
this->_line->setText("test");
with no dialog also crashes ?Instead this works!
BUT:this also works:
connect(_btn, &QToolButton::clicked, [this]() { QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)")); });while this crashes:
connect(_btn, &QToolButton::clicked, [this]() { QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)")); this->_line->setText("test"); });Does this:
connect(_btn, &QToolButton::clicked, this, [this] () -> void { QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)")); _line->setText("test"); });crash?
From the behaviour described it does seem you have a dangling pointer/reference. Also don't do that:
SignatureEditor *widget = static_cast<SignatureEditor *>(editor);without at least having a debug-time check on it:
Q_ASSERT(qobject_cast<SignatureEditor *>(editor)); SignatureEditor *widget = static_cast<SignatureEditor *>(editor); -
Does this:
connect(_btn, &QToolButton::clicked, this, [this] () -> void { QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)")); _line->setText("test"); });crash?
From the behaviour described it does seem you have a dangling pointer/reference. Also don't do that:
SignatureEditor *widget = static_cast<SignatureEditor *>(editor);without at least having a debug-time check on it:
Q_ASSERT(qobject_cast<SignatureEditor *>(editor)); SignatureEditor *widget = static_cast<SignatureEditor *>(editor);@kshegunov said in "Undebuggable" segmentation fault:
Does this:
connect(_btn, &QToolButton::clicked, this, [this] () -> void { QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)")); _line->setText("test"); });crash?
Yes, it crashes.
From the behaviour described it does seem you have dangling pointer/reference. Also don't do that:
without at least having a debug time check on it:We've already checked the pointers and are not null.
-
@kshegunov said in "Undebuggable" segmentation fault:
Does this:
connect(_btn, &QToolButton::clicked, this, [this] () -> void { QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)")); _line->setText("test"); });crash?
Yes, it crashes.
From the behaviour described it does seem you have dangling pointer/reference. Also don't do that:
without at least having a debug time check on it:We've already checked the pointers and are not null.
@Mark81 said in "Undebuggable" segmentation fault:
Yes, it crashes.
Please break before the
QLineEdit::setTextand extract the backtrace for the thread.We've already checked the pointers and are not null.
static_castdoes not check if the types involved behind the pointer are compatible or convertible, so whether the pointer's null or not is meaningless if the typing is wrong. -
Hi
Shit i read
SignatureEditor *widget = static_cast<SignatureEditor *>(editor);
as qobject_cast
so good catch, its most likely that. -
Hi
Shit i read
SignatureEditor *widget = static_cast<SignatureEditor *>(editor);
as qobject_cast
so good catch, its most likely that.@mrjj said in "Undebuggable" segmentation fault:
as qobject_cast
so good catch, its most likely that.I changed all
static_casttoqobject_castwith no differences.@kshegunov
here we are:
-
@mrjj said in "Undebuggable" segmentation fault:
as qobject_cast
so good catch, its most likely that.I changed all
static_casttoqobject_castwith no differences.@kshegunov
here we are:@Mark81 said in "Undebuggable" segmentation fault:
here we are:
Two problems with the screenshot:
- I can't see the whole stack (including the root), more important. Use right click and from the context menu extract it as text please.
- You didn't specify a context object for the lambda, which I requested in my previous post.
-
@Mark81 said in "Undebuggable" segmentation fault:
here we are:
Two problems with the screenshot:
- I can't see the whole stack (including the root), more important. Use right click and from the context menu extract it as text please.
- You didn't specify a context object for the lambda, which I requested in my previous post.
@kshegunov said in "Undebuggable" segmentation fault:
Two problems with the screenshot:
- I can't see the whole stack (including the root), more important. Use right click and from the context menu extract it as text please.
- You didn't specify a context object for the lambda, which I requested in my previous post.
Sorry Sir, but we made a lot of trials. I wasn't sure about which code you want. By the way it's another syntax, very different! Why? Here the update screenshot and text:
Full backtrace attached as it's too big for the post. Here just the same info extracted as text:
1 SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}::operator()() const customdelegateoperators.h 37 0x492bb0 2 QtPrivate::FunctorCall<QtPrivate::IndexesList<>, QtPrivate::List<>, void, SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}>::call({lambda()#1}&, void * *) qobjectdefs_impl.h 128 0x48739a 3 QtPrivate::Functor<SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}, 0>::call<QtPrivate::List<>, void>({lambda()#1}&, void *, {lambda()#1}& *) qobjectdefs_impl.h 238 0x48bf44 4 QtPrivate::QFunctorSlotObject<SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}, 0, QtPrivate::List<>, void>::impl(int, QtPrivate::QSlotObjectBase *, QObject *, void * *, bool *) qobjectdefs_impl.h 421 0x48ba8d 5 QtPrivate::QSlotObjectBase::call qobjectdefs_impl.h 376 0x281c173 6 QMetaObject::activate qobject.cpp 3754 0x281c173 7 QMetaObject::activate qobject.cpp 3633 0x281c575 8 QAbstractButton::clicked moc_qabstractbutton.cpp 308 0x1b48b7ac 9 QAbstractButtonPrivate::emitClicked qabstractbutton.cpp 414 0x1b48b9d5 10 QAbstractButtonPrivate::click qabstractbutton.cpp 407 0x1b48d17a 11 QAbstractButton::mouseReleaseEvent qabstractbutton.cpp 1011 0x1b48d3aa 12 QToolButton::mouseReleaseEvent qtoolbutton.cpp 622 0x1b576fd1 13 QWidget::event qwidget.cpp 8901 0x1b3db0e0 14 QAbstractButton::event qabstractbutton.cpp 968 0x1b48e7bc 15 QToolButton::event qtoolbutton.cpp 985 0x1b57711e 16 QApplicationPrivate::notify_helper qapplication.cpp 3727 0x1b3985ca 17 QApplication::notify qapplication.cpp 3203 0x1b3a0107 18 QCoreApplication::notifyInternal2 qcoreapplication.cpp 1048 0x27f5119 19 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 237 0x1b39f077 20 QApplicationPrivate::sendMouseEvent qapplication.cpp 2693 0x1b39f077 21 QWidgetWindow::handleMouseEvent qwidgetwindow.cpp 660 0x1b3f1af4 22 QWidgetWindow::event qwidgetwindow.cpp 281 0x1b3f3bf9 23 QApplicationPrivate::notify_helper qapplication.cpp 3727 0x1b3985ca 24 QApplication::notify qapplication.cpp 3099 0x1b39fb83 25 QCoreApplication::notifyInternal2 qcoreapplication.cpp 1048 0x27f5119 26 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 237 0x99cabfc 27 QGuiApplicationPrivate::processMouseEvent qguiapplication.cpp 2081 0x99cabfc 28 QGuiApplicationPrivate::processWindowSystemEvent qguiapplication.cpp 1816 0x99cc4d7 29 QWindowSystemInterface::sendWindowSystemEvents qwindowsysteminterface.cpp 1032 0x99adf99 30 QWindowsGuiEventDispatcher::sendPostedEvents qwindowsguieventdispatcher.cpp 82 0x2883dae4 31 qt_internal_proc(HWND__ *, unsigned int, unsigned int, long) *16 qeventdispatcher_win.cpp 237 0x284538d 32 gapfnScSendMessage 0x769f62fa 33 ?? 0x62047e 34 USER32!GetThreadDesktop 0x769f6d3a 35 QEventDispatcherWin32Private::sendTimerEvent qeventdispatcher_win.cpp 456 0x2844dc9 36 ?? 0x62047e 37 USER32!CharPrevW 0x769f77c4 38 USER32!DispatchMessageW 0x769f788a 39 QEventDispatcherWin32::processEvents qeventdispatcher_win.cpp 629 0x2844ae8 40 QWindowsGuiEventDispatcher::processEvents qwindowsguieventdispatcher.cpp 74 0x2883dab7 41 QEventLoop::processEvents qeventloop.cpp 136 0x27f37c8 42 QEventLoop::exec qeventloop.cpp 214 0x27f3c20 43 QDialog::exec qdialog.cpp 546 0x1b5907de 44 MainWindow::on_actionImpostazioni_triggered mainwindow.cpp 1518 0x40e152 45 MainWindow::qt_static_metacall moc_mainwindow.cpp 298 0x43f973 46 MainWindow::qt_metacall moc_mainwindow.cpp 368 0x43fcc2 47 QMetaObject::metacall qmetaobject.cpp 301 0x27fe365 48 QMetaObject::activate qobject.cpp 3786 0x281c37f 49 QMetaObject::activate qobject.cpp 3633 0x281c575 50 QAction::triggered moc_qaction.cpp 376 0x1b391618 51 QAction::activate qaction.cpp 1167 0x1b394579 52 QMenuPrivate::activateCausedStack qmenu.cpp 1371 0x1b50d432 53 QMenuPrivate::activateAction qmenu.cpp 1448 0x1b51507e 54 QMenu::mouseReleaseEvent qmenu.cpp 2942 0x1b515c07 55 QWidget::event qwidget.cpp 8901 0x1b3db0e0 56 QMenu::event qmenu.cpp 3064 0x1b5180de 57 QApplicationPrivate::notify_helper qapplication.cpp 3727 0x1b3985ca 58 QApplication::notify qapplication.cpp 3203 0x1b3a0107 59 QCoreApplication::notifyInternal2 qcoreapplication.cpp 1048 0x27f5119 60 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 237 0x1b39f077 61 QApplicationPrivate::sendMouseEvent qapplication.cpp 2693 0x1b39f077 62 QWidgetWindow::handleMouseEvent qwidgetwindow.cpp 556 0x1b3f0ed3 63 QWidgetWindow::event qwidgetwindow.cpp 281 0x1b3f3bf9 64 QApplicationPrivate::notify_helper qapplication.cpp 3727 0x1b3985ca 65 QApplication::notify qapplication.cpp 3099 0x1b39fb83 66 QCoreApplication::notifyInternal2 qcoreapplication.cpp 1048 0x27f5119 67 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 237 0x99cabfc 68 QGuiApplicationPrivate::processMouseEvent qguiapplication.cpp 2081 0x99cabfc 69 QGuiApplicationPrivate::processWindowSystemEvent qguiapplication.cpp 1816 0x99cc4d7 70 QWindowSystemInterface::sendWindowSystemEvents qwindowsysteminterface.cpp 1032 0x99adf99 71 QWindowsGuiEventDispatcher::sendPostedEvents qwindowsguieventdispatcher.cpp 82 0x2883dae4 72 qt_internal_proc(HWND__ *, unsigned int, unsigned int, long) *16 qeventdispatcher_win.cpp 237 0x284538d 73 gapfnScSendMessage 0x769f62fa 74 ?? 0x62047e 75 USER32!GetThreadDesktop 0x769f6d3a 76 QEventDispatcherWin32Private::sendTimerEvent qeventdispatcher_win.cpp 456 0x2844dc9 77 ?? 0x62047e 78 USER32!CharPrevW 0x769f77c4 79 USER32!DispatchMessageW 0x769f788a 80 QEventDispatcherWin32::processEvents qeventdispatcher_win.cpp 629 0x2844ae8 81 QWindowsGuiEventDispatcher::processEvents qwindowsguieventdispatcher.cpp 74 0x2883dab7 82 QEventLoop::processEvents qeventloop.cpp 136 0x27f37c8 83 QEventLoop::exec qeventloop.cpp 214 0x27f3c20 84 QCoreApplication::exec qcoreapplication.cpp 1336 0x27fc30e 85 QGuiApplication::exec qguiapplication.cpp 1761 0x99c1552 86 QApplication::exec qapplication.cpp 2901 0x1b3984a9 87 qMain main.cpp 37 0x401859 88 WinMain *16 qtmain_win.cpp 104 0x447465 89 main 0x49883d [0_1548258146048_backtrace.txt](Uploading 100%) -
Hi
Just to be 100% sure.
You still have the checks at your casts, right ?SignatureEditor *widget = qobject_cast<SignatureEditor *>(editor); // Note qobject_cast ! if (widget) { widget->setText(value); widget->activate(); } else qDebug() << "invalid cast for editor"; -
@kshegunov said in "Undebuggable" segmentation fault:
Two problems with the screenshot:
- I can't see the whole stack (including the root), more important. Use right click and from the context menu extract it as text please.
- You didn't specify a context object for the lambda, which I requested in my previous post.
Sorry Sir, but we made a lot of trials. I wasn't sure about which code you want. By the way it's another syntax, very different! Why? Here the update screenshot and text:
Full backtrace attached as it's too big for the post. Here just the same info extracted as text:
1 SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}::operator()() const customdelegateoperators.h 37 0x492bb0 2 QtPrivate::FunctorCall<QtPrivate::IndexesList<>, QtPrivate::List<>, void, SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}>::call({lambda()#1}&, void * *) qobjectdefs_impl.h 128 0x48739a 3 QtPrivate::Functor<SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}, 0>::call<QtPrivate::List<>, void>({lambda()#1}&, void *, {lambda()#1}& *) qobjectdefs_impl.h 238 0x48bf44 4 QtPrivate::QFunctorSlotObject<SignatureEditor::SignatureEditor(QWidget *)::{lambda()#1}, 0, QtPrivate::List<>, void>::impl(int, QtPrivate::QSlotObjectBase *, QObject *, void * *, bool *) qobjectdefs_impl.h 421 0x48ba8d 5 QtPrivate::QSlotObjectBase::call qobjectdefs_impl.h 376 0x281c173 6 QMetaObject::activate qobject.cpp 3754 0x281c173 7 QMetaObject::activate qobject.cpp 3633 0x281c575 8 QAbstractButton::clicked moc_qabstractbutton.cpp 308 0x1b48b7ac 9 QAbstractButtonPrivate::emitClicked qabstractbutton.cpp 414 0x1b48b9d5 10 QAbstractButtonPrivate::click qabstractbutton.cpp 407 0x1b48d17a 11 QAbstractButton::mouseReleaseEvent qabstractbutton.cpp 1011 0x1b48d3aa 12 QToolButton::mouseReleaseEvent qtoolbutton.cpp 622 0x1b576fd1 13 QWidget::event qwidget.cpp 8901 0x1b3db0e0 14 QAbstractButton::event qabstractbutton.cpp 968 0x1b48e7bc 15 QToolButton::event qtoolbutton.cpp 985 0x1b57711e 16 QApplicationPrivate::notify_helper qapplication.cpp 3727 0x1b3985ca 17 QApplication::notify qapplication.cpp 3203 0x1b3a0107 18 QCoreApplication::notifyInternal2 qcoreapplication.cpp 1048 0x27f5119 19 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 237 0x1b39f077 20 QApplicationPrivate::sendMouseEvent qapplication.cpp 2693 0x1b39f077 21 QWidgetWindow::handleMouseEvent qwidgetwindow.cpp 660 0x1b3f1af4 22 QWidgetWindow::event qwidgetwindow.cpp 281 0x1b3f3bf9 23 QApplicationPrivate::notify_helper qapplication.cpp 3727 0x1b3985ca 24 QApplication::notify qapplication.cpp 3099 0x1b39fb83 25 QCoreApplication::notifyInternal2 qcoreapplication.cpp 1048 0x27f5119 26 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 237 0x99cabfc 27 QGuiApplicationPrivate::processMouseEvent qguiapplication.cpp 2081 0x99cabfc 28 QGuiApplicationPrivate::processWindowSystemEvent qguiapplication.cpp 1816 0x99cc4d7 29 QWindowSystemInterface::sendWindowSystemEvents qwindowsysteminterface.cpp 1032 0x99adf99 30 QWindowsGuiEventDispatcher::sendPostedEvents qwindowsguieventdispatcher.cpp 82 0x2883dae4 31 qt_internal_proc(HWND__ *, unsigned int, unsigned int, long) *16 qeventdispatcher_win.cpp 237 0x284538d 32 gapfnScSendMessage 0x769f62fa 33 ?? 0x62047e 34 USER32!GetThreadDesktop 0x769f6d3a 35 QEventDispatcherWin32Private::sendTimerEvent qeventdispatcher_win.cpp 456 0x2844dc9 36 ?? 0x62047e 37 USER32!CharPrevW 0x769f77c4 38 USER32!DispatchMessageW 0x769f788a 39 QEventDispatcherWin32::processEvents qeventdispatcher_win.cpp 629 0x2844ae8 40 QWindowsGuiEventDispatcher::processEvents qwindowsguieventdispatcher.cpp 74 0x2883dab7 41 QEventLoop::processEvents qeventloop.cpp 136 0x27f37c8 42 QEventLoop::exec qeventloop.cpp 214 0x27f3c20 43 QDialog::exec qdialog.cpp 546 0x1b5907de 44 MainWindow::on_actionImpostazioni_triggered mainwindow.cpp 1518 0x40e152 45 MainWindow::qt_static_metacall moc_mainwindow.cpp 298 0x43f973 46 MainWindow::qt_metacall moc_mainwindow.cpp 368 0x43fcc2 47 QMetaObject::metacall qmetaobject.cpp 301 0x27fe365 48 QMetaObject::activate qobject.cpp 3786 0x281c37f 49 QMetaObject::activate qobject.cpp 3633 0x281c575 50 QAction::triggered moc_qaction.cpp 376 0x1b391618 51 QAction::activate qaction.cpp 1167 0x1b394579 52 QMenuPrivate::activateCausedStack qmenu.cpp 1371 0x1b50d432 53 QMenuPrivate::activateAction qmenu.cpp 1448 0x1b51507e 54 QMenu::mouseReleaseEvent qmenu.cpp 2942 0x1b515c07 55 QWidget::event qwidget.cpp 8901 0x1b3db0e0 56 QMenu::event qmenu.cpp 3064 0x1b5180de 57 QApplicationPrivate::notify_helper qapplication.cpp 3727 0x1b3985ca 58 QApplication::notify qapplication.cpp 3203 0x1b3a0107 59 QCoreApplication::notifyInternal2 qcoreapplication.cpp 1048 0x27f5119 60 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 237 0x1b39f077 61 QApplicationPrivate::sendMouseEvent qapplication.cpp 2693 0x1b39f077 62 QWidgetWindow::handleMouseEvent qwidgetwindow.cpp 556 0x1b3f0ed3 63 QWidgetWindow::event qwidgetwindow.cpp 281 0x1b3f3bf9 64 QApplicationPrivate::notify_helper qapplication.cpp 3727 0x1b3985ca 65 QApplication::notify qapplication.cpp 3099 0x1b39fb83 66 QCoreApplication::notifyInternal2 qcoreapplication.cpp 1048 0x27f5119 67 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 237 0x99cabfc 68 QGuiApplicationPrivate::processMouseEvent qguiapplication.cpp 2081 0x99cabfc 69 QGuiApplicationPrivate::processWindowSystemEvent qguiapplication.cpp 1816 0x99cc4d7 70 QWindowSystemInterface::sendWindowSystemEvents qwindowsysteminterface.cpp 1032 0x99adf99 71 QWindowsGuiEventDispatcher::sendPostedEvents qwindowsguieventdispatcher.cpp 82 0x2883dae4 72 qt_internal_proc(HWND__ *, unsigned int, unsigned int, long) *16 qeventdispatcher_win.cpp 237 0x284538d 73 gapfnScSendMessage 0x769f62fa 74 ?? 0x62047e 75 USER32!GetThreadDesktop 0x769f6d3a 76 QEventDispatcherWin32Private::sendTimerEvent qeventdispatcher_win.cpp 456 0x2844dc9 77 ?? 0x62047e 78 USER32!CharPrevW 0x769f77c4 79 USER32!DispatchMessageW 0x769f788a 80 QEventDispatcherWin32::processEvents qeventdispatcher_win.cpp 629 0x2844ae8 81 QWindowsGuiEventDispatcher::processEvents qwindowsguieventdispatcher.cpp 74 0x2883dab7 82 QEventLoop::processEvents qeventloop.cpp 136 0x27f37c8 83 QEventLoop::exec qeventloop.cpp 214 0x27f3c20 84 QCoreApplication::exec qcoreapplication.cpp 1336 0x27fc30e 85 QGuiApplication::exec qguiapplication.cpp 1761 0x99c1552 86 QApplication::exec qapplication.cpp 2901 0x1b3984a9 87 qMain main.cpp 37 0x401859 88 WinMain *16 qtmain_win.cpp 104 0x447465 89 main 0x49883d [0_1548258146048_backtrace.txt](Uploading 100%)@Mark81 said in "Undebuggable" segmentation fault:
Sorry Sir, but we made a lot of trials. I wasn't sure about which code you want. By the way it's another syntax, very different! Why?
No need for the formality. This overload of the connect makes sure that
thisexists at the point of the lambda call, the other doesn't that's why I wanted it specifically. The connection will be broken ifthisgets destroyed between theconnectcall and the actual lambda call, which isn't true for the overload without the context object.Full backtrace attached as it's too big for the post. Here just the same info extracted as text:
This is perfectly fine, I was interested exactly in this one, the other threads are not interesting at this point. The trace looks okay.
Humor me once again, and substitute the:
QDialog myDialog; // ... myDialog.exec()you have in your
MainWindow::on_actionImpostazioni_triggeredslot with:QDialog * myDialog = new QDialog(); // ... myDialog->show();See if that makes a difference.
Also, could you print out the addresses of the variables involved in the lambda (you can see them in the "Application output pane" when you run the app), something like this:
connect(_btn, &QToolButton::clicked, this, [this] () -> void { QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)")); qDebug() << this << _btn << _line; _line->setText("test"); });(You'd need to include
<QDebug>for this)One more thing you could try is to add one guarded pointer to the
_linepointer so you're 100% it's not destroyed in the mean time. It'd look like this:QPointer<QLineEdit> testPointer(_line); connect(_btn, &QToolButton::clicked, this, [this, testPointer] () -> void { QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)")); qDebug() << this << _btn << _line << testPointer; _line->setText("test"); }); -
@Mark81 said in "Undebuggable" segmentation fault:
Sorry Sir, but we made a lot of trials. I wasn't sure about which code you want. By the way it's another syntax, very different! Why?
No need for the formality. This overload of the connect makes sure that
thisexists at the point of the lambda call, the other doesn't that's why I wanted it specifically. The connection will be broken ifthisgets destroyed between theconnectcall and the actual lambda call, which isn't true for the overload without the context object.Full backtrace attached as it's too big for the post. Here just the same info extracted as text:
This is perfectly fine, I was interested exactly in this one, the other threads are not interesting at this point. The trace looks okay.
Humor me once again, and substitute the:
QDialog myDialog; // ... myDialog.exec()you have in your
MainWindow::on_actionImpostazioni_triggeredslot with:QDialog * myDialog = new QDialog(); // ... myDialog->show();See if that makes a difference.
Also, could you print out the addresses of the variables involved in the lambda (you can see them in the "Application output pane" when you run the app), something like this:
connect(_btn, &QToolButton::clicked, this, [this] () -> void { QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)")); qDebug() << this << _btn << _line; _line->setText("test"); });(You'd need to include
<QDebug>for this)One more thing you could try is to add one guarded pointer to the
_linepointer so you're 100% it's not destroyed in the mean time. It'd look like this:QPointer<QLineEdit> testPointer(_line); connect(_btn, &QToolButton::clicked, this, [this, testPointer] () -> void { QString filename = QFileDialog::getOpenFileName(nullptr, tr("Select signature image"), QDir::homePath(), tr("Portable Network Graphics (*.png)")); qDebug() << this << _btn << _line << testPointer; _line->setText("test"); });@kshegunov thanks for the detailed answer and for your effort.
The debugger says "no valid expression" for everything inside the lambda function, is it normal?Let's summarize:
qDebug() << this << _btn << _line;leads to a SIGSEGVqDebug() << this << _btn << _line << testPointer;leads to SIGILLqDebug() << _btn << _line;leads also to a SIGSEGVbut removing the file dialog call:
QPointer<QLineEdit> testPointer(_line); connect(_btn, &QToolButton::clicked, this, [this, testPointer] () -> void { qDebug() << this << _btn << _line << testPointer; _line->setText("test"); });prints out:
SignatureEditor(0x2f09b430) QToolButton(0x2e1910b0) QLineEdit(0x2e2e13e0) QLineEdit(0x2e2e13e0)
-
@kshegunov thanks for the detailed answer and for your effort.
The debugger says "no valid expression" for everything inside the lambda function, is it normal?Let's summarize:
qDebug() << this << _btn << _line;leads to a SIGSEGVqDebug() << this << _btn << _line << testPointer;leads to SIGILLqDebug() << _btn << _line;leads also to a SIGSEGVbut removing the file dialog call:
QPointer<QLineEdit> testPointer(_line); connect(_btn, &QToolButton::clicked, this, [this, testPointer] () -> void { qDebug() << this << _btn << _line << testPointer; _line->setText("test"); });prints out:
SignatureEditor(0x2f09b430) QToolButton(0x2e1910b0) QLineEdit(0x2e2e13e0) QLineEdit(0x2e2e13e0)
@Mark81 said in "Undebuggable" segmentation fault:
The debugger says "no valid expression" for everything inside the lambda function, is it normal?
Not really. What compiler, debugger are you using and what are their versions? Just the other day I had stumbled on a bug in one specific version of MSVC's code generation where it didn't properly copy objects that are passed by value in the lambda capture.
but removing the file dialog call:
[snip]
prints out:The addresses are good. So for some reason the file dialog invalidates the object(s). This can happen in principle, depending on event order, because the static function spins the event loop. Can you try something else then (same idea):
connect(_btn, &QToolButton::clicked, this, [this] () -> void { // Here use the non-static way of opening the dialog QFileDialog * myDialog = new QFileDialog(); QObject::connect(myDialog, &QDialog::accepted, this, [this] () -> void { qDebug() << "If we see this message it's all good, otherwise `this` is deleted through `QDialog::exec`"; }); myDialog->show(); //_line->setText("test"); });Edit: Updated code, because I forgot to add the context parameter for
connect
