Error accesing private member of a class inside a shared library
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Please provide some more code, with the complete call stack. Also do you use the same Qt version for your dll and your app?
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@Christian-Ehrlicher , the code The code is the one I have set. Just add that the Shape constructor is the default constructor: Shape() = default;. I have put the call stack above.
But, as I said, I think the code has no problems (as you can see it is very simple). This code worked perfectly until recently. In addition, the same thing is happening to me with other classes within the shared library. It must be something of project configuration, compiler configuration (MSVC 2017 64-bit) or something similar. I have quite a bit of experience programming in C++ and Qt in particular, and it's the first time I've come across a problem as simple and as absurd as this.
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By way of summary, and to clarify the problem:
In shared library:
class SHAPE_EXPORT Shape { private: QString m_name; ... } bool Shape::open(const QString &name) { m_name = name; ... }After invoking by:
Shape shape; if (!shape.open("locations.shp")) { ...The line m_name = name throws an exception:
Stopped in thread 0 by Exception at 0x7ffe3d83185d, code 0x0000005: read access violation at: 0x0, flags=0x0 (first chance).And the call stack:
1 std::_Load_relaxed_4 2 std::_Atomic_load_4 3 std::atomic_load_explicit 4 std::_Atomic_int::load 5 QAtomicOps<int>::loadRelaxed<int> 6 QBasicAtomicInteger<int>::loadRelaxed 7 QtPrivate::RefCount::deref 8 QString::operator= 9 Shape::openIf I change the library code to:
class SHAPE_EXPORT Shape { private: QString m_name; ... } bool Shape::open(const QString &name) { qDebug() << m_name; ... }The same exception occurs. The call stack is now:
1 QString::length 2 QDebug::operator<< 3 Shape::openAccess to int-type variables does not cause exceptions.
All the code (main program and shared library) are made qith Qt 5.14.2 with MSVC 2017 64bits. The .pro of the shared library is:
QT += core gui greaterThan(QT_MAJOR_VERSION, 4): QT += widgets CONFIG += qt windows no_batch win32:CONFIG += debug_and_release build_all CONFIG += shared CONFIG += c++17 CONFIG += install_headers TEMPLATE = lib INCLUDEPATH += .. win32 { QMAKE_CXXFLAGS += -utf-8 DEFINES += WIN32_LEAN_AND_MEAN _USE_MATH_DEFINES NOMINMAX _CRT_SECURE_NO_WARNINGS } TARGET = $$qtLibraryTarget(Shape) include(shape.pri) INSTALL_HEADERS = $$HEADERS INSTALL_HEADERS -= $$PRIVATE_HEADERS INSTALL_PREFIX = $$[QT_INSTALL_HEADERS]/shape dlltarget.path = $$[QT_INSTALL_BINS] INSTALLS += dlltarget target.path = $$[QT_INSTALL_LIBS] target.CONFIG = no_dll INSTALLS += targetI think the code has no problems. Can be some configuration problem?
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@JR-Leal said in Error accesing private member of a class inside a shared library:
In this code you have repeated several times now:
class SHAPE_EXPORT Shape { private: QString m_name; ... } bool open(const QString &name) { qDebug() << m_name; ... }The function
open()is not a member of Shape and therefore barred from accessing private member variables in that class. If this is actually your code it should fail to compile with a clear error message.You appear to have something that compiles and can be run with a backtrace involving
Shape::open().
You should share your actual code. -
@ChrisW67 I'm sorry. The code is:
bool Shape::open(const QString &name)My code is much more complex. I have write only a extract of it.
- I have fixed the occurrences of this member function in previous posts for greater code clarity
@JR-Leal said in Error accesing private member of a class inside a shared library:
My code is much more complex. I have write only a extract of it.
Yes, and by the look of the stack trace you're calling a method on an uninitialized object, looks like calling a dangling pointer.
I'm pretty sure this:Shape shape; if (!shape.open("locations.shp")) {Isn't how the call is made.
I'll repeat what others have asked: Provide more code, a complete example that (re)produces the problem. -
@JR-Leal said in Error accesing private member of a class inside a shared library:
My code is much more complex. I have write only a extract of it.
Yes, and by the look of the stack trace you're calling a method on an uninitialized object, looks like calling a dangling pointer.
I'm pretty sure this:Shape shape; if (!shape.open("locations.shp")) {Isn't how the call is made.
I'll repeat what others have asked: Provide more code, a complete example that (re)produces the problem.@kshegunov This code is just as I have put. Although it seems absurd, such simple pieces of code generate that exception, if the Shape class is in a shared library. If I use it directly (without libraries) the code works well.
In addition, the code worked perfectly and I have not modified it. This same problem has happened to me in other classes of the shared library. That's why I think it's a configuration problem.Shape shape; if (!shape.open("locations.shp")) {This portion of code is 100% equal to my code.
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@kshegunov This code is just as I have put. Although it seems absurd, such simple pieces of code generate that exception, if the Shape class is in a shared library. If I use it directly (without libraries) the code works well.
In addition, the code worked perfectly and I have not modified it. This same problem has happened to me in other classes of the shared library. That's why I think it's a configuration problem.Shape shape; if (!shape.open("locations.shp")) {This portion of code is 100% equal to my code.
@JR-Leal said in Error accesing private member of a class inside a shared library:
This code is just as I have put. Although it seems absurd, such simple pieces of code generate that exception, if the Shape class is in a shared library. If I use it directly (without libraries) the code works well.
Fine. The fact remains that the top of the call stack looks like a dereferencing an invalid address. Show a full stack trace of the crash (and I don't just mean one staring from
::open); I want to see the bottom of the call stack. And with file names and line numbers. -
@JR-Leal said in Error accesing private member of a class inside a shared library:
This code is just as I have put. Although it seems absurd, such simple pieces of code generate that exception, if the Shape class is in a shared library. If I use it directly (without libraries) the code works well.
Fine. The fact remains that the top of the call stack looks like a dereferencing an invalid address. Show a full stack trace of the crash (and I don't just mean one staring from
::open); I want to see the bottom of the call stack. And with file names and line numbers.@kshegunov Here you have both stacks. One with qDebug() << m_name;
and one with m_name = name:
It is clear to me that the error seems to be trying to access an uninitialized object, but this is not the case. In fact, I can access other properties of type int, bool, without problems.
And I repeat, at the risk of sounding heavy, that the same thing is happening to me with other classes within the shared library, when until not long ago they worked perfectly.
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@kshegunov Here you have both stacks. One with qDebug() << m_name;
and one with m_name = name:
It is clear to me that the error seems to be trying to access an uninitialized object, but this is not the case. In fact, I can access other properties of type int, bool, without problems.
And I repeat, at the risk of sounding heavy, that the same thing is happening to me with other classes within the shared library, when until not long ago they worked perfectly.
@JR-Leal said in Error accesing private member of a class inside a shared library:
when until not long ago they worked perfectly.
Then what changed "not long ago"?
Have you thrown away the build directory to be absolutely sure you have a clean build without mismatched components?
Since your code is inside a shared library:
Did you change the binary interface of any of the the classes involved in your library?
Have you rebuilt the executable you are running against the freshly built library? -
@kshegunov Here you have both stacks. One with qDebug() << m_name;
and one with m_name = name:
It is clear to me that the error seems to be trying to access an uninitialized object, but this is not the case. In fact, I can access other properties of type int, bool, without problems.
And I repeat, at the risk of sounding heavy, that the same thing is happening to me with other classes within the shared library, when until not long ago they worked perfectly.
@JR-Leal said in Error accesing private member of a class inside a shared library:
@kshegunov Here you have both stacks.
Thank you, I'm interested only in the one generated by the assignment, however it is incomplete. I asked that the bottom of the stack should be visible. What I see here is that this is called in a
textChangedsignal handler and not much more. I'd rather be able to trace the whole call chain ...It is clear to me that the error seems to be trying to access an uninitialized object, but this is not the case. In fact, I can access other properties of type int, bool, without problems.
This means absolutely nothing. You can read primitive types from unowned memory all you want. If the value that they the memory had held was what you expected, you'd even read sensible values ...
And I repeat, at the risk of sounding heavy, that the same thing is happening to me with other classes within the shared library, when until not long ago they worked perfectly.
Fine. Then what @ChrisW67 asked - something changed, so what did?
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@ChrisW67 , @kshegunov The problem is that I have changed many things. The software has been constantly evolving. And now I've been notified of this error, and I've been told that it's been a long time since it's been a while. In addition to fixing bugs, improving functionality and adding new ones, I have changed from C++14 to C++17 in the compiler options (but I have not changed the compiler version, it is still MSVC 2017 64-bit). I do not remember changing any other options (and in subversion I have not found other modifications).
I'm going to try creating a new, extremely simple class in the shared library and see if it gives me the same problems.
As for the call stack, it is very long. The event is triggered inside a dialog box, so there is previously the creation part of it. Here you can see the following lines:
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@ChrisW67 , @kshegunov The problem is that I have changed many things. The software has been constantly evolving. And now I've been notified of this error, and I've been told that it's been a long time since it's been a while. In addition to fixing bugs, improving functionality and adding new ones, I have changed from C++14 to C++17 in the compiler options (but I have not changed the compiler version, it is still MSVC 2017 64-bit). I do not remember changing any other options (and in subversion I have not found other modifications).
I'm going to try creating a new, extremely simple class in the shared library and see if it gives me the same problems.
As for the call stack, it is very long. The event is triggered inside a dialog box, so there is previously the creation part of it. Here you can see the following lines:
@JR-Leal said in Error accesing private member of a class inside a shared library:
As for the call stack, it is very long. The event is triggered inside a dialog box, so there is previously the creation part of it. Here you can see the following lines:
Yes, I suggest you extract it as text from Creator. ;)
Do you mind showing what sits around (5-10 lines before and after) line 31 inMenuHerramientas.cpp, where you open the dialog. Also put a breakpoint in the dialog destructor to make sure. Additionally, please show the lambda (exactly as it appears in the code) that's connected to theclickedsignal, the one that callsQLineEdit::setText. -
@JR-Leal said in Error accesing private member of a class inside a shared library:
As for the call stack, it is very long. The event is triggered inside a dialog box, so there is previously the creation part of it. Here you can see the following lines:
Yes, I suggest you extract it as text from Creator. ;)
Do you mind showing what sits around (5-10 lines before and after) line 31 inMenuHerramientas.cpp, where you open the dialog. Also put a breakpoint in the dialog destructor to make sure. Additionally, please show the lambda (exactly as it appears in the code) that's connected to theclickedsignal, the one that callsQLineEdit::setText.@kshegunov It hadn't occurred to me that you can copy the contents of the call stack as text, sorry.
Complete call stack:
1 std::_Load_relaxed_4 xatomic.h 1341 0x7ffe3d62a87e 2 std::_Atomic_load_4 xatomic.h 1360 0x7ffe3d629aed 3 std::atomic_load_explicit xxatomic 495 0x7ffe3d62c9d7 4 std::_Atomic_int::load xxatomic 630 0x7ffe3d6318ab 5 QAtomicOps<int>::loadRelaxed<int> qatomic_cxx11.h 240 0x7ffe3d624a25 6 QBasicAtomicInteger<int>::loadRelaxed qbasicatomic.h 107 0x7ffe3d6318d6 7 QtPrivate::RefCount::deref qrefcount.h 66 0x7ffe3d62ee66 8 QString::operator= qstring.cpp 2398 0x7ffe3d84aed2 9 amatel::Shape::abre Shape.cpp 88 0x7ffee76f3c6f 10 DlgShp2Tif::onTextChanged DlgShp2Tif.cpp 220 0x7ff6a7776f09 11 QtPrivate::FunctorCall<QtPrivate::IndexesList<0>,QtPrivate::List<QString const &>,void,void (__cdecl DlgShp2Tif:: *)(QString const &)>::call qobjectdefs_impl.h 152 0x7ff6a777c4ae 12 QtPrivate::FunctionPointer<void (__cdecl DlgShp2Tif:: *)(QString const &)>::call<QtPrivate::List<QString const &>,void> qobjectdefs_impl.h 186 0x7ff6a7778d3d 13 QtPrivate::QSlotObject<void (__cdecl DlgShp2Tif:: *)(QString const &),QtPrivate::List<QString const &>,void>::impl qobjectdefs_impl.h 419 0x7ff6a777d21d 14 QtPrivate::QSlotObjectBase::call qobjectdefs_impl.h 398 0x7ffe3daccd22 15 doActivate<0> qobject.cpp 3870 0x7ffe3db2548c 16 QMetaObject::activate qobject.cpp 3931 0x7ffe3db12d77 17 QLineEdit::textChanged moc_qlineedit.cpp 448 0x7ffe3f5e9110 18 QLineEdit::qt_static_metacall moc_qlineedit.cpp 255 0x7ffe3f5e4542 19 doActivate<0> qobject.cpp 3885 0x7ffe3db255a3 20 QMetaObject::activate qobject.cpp 3931 0x7ffe3db12d77 21 QWidgetLineControl::textChanged moc_qwidgetlinecontrol_p.cpp 274 0x7ffe3f5f8ac3 22 QWidgetLineControl::finishChange qwidgetlinecontrol.cpp 737 0x7ffe3f5f61c1 23 QWidgetLineControl::internalSetText qwidgetlinecontrol.cpp 772 0x7ffe3f5f4559 24 QWidgetLineControl::setText qwidgetlinecontrol_p.h 252 0x7ffe3f580126 25 QLineEditPrivate::setText qlineedit_p.cpp 277 0x7ffe3f5dde57 26 QLineEdit::setText qlineedit.cpp 319 0x7ffe3f5e749c 27 <lambda_98a6b26bf0d27f8737cd826cc5a9a62a>::operator() DlgShp2Tif.cpp 58 0x7ff6a777b6c0 28 QtPrivate::FunctorCall<QtPrivate::IndexesList<>,QtPrivate::List<>,void,<lambda_98a6b26bf0d27f8737cd826cc5a9a62a>>::call qobjectdefs_impl.h 146 0x7ff6a777c8a8 29 QtPrivate::Functor<<lambda_98a6b26bf0d27f8737cd826cc5a9a62a>,0>::call<QtPrivate::List<>,void> qobjectdefs_impl.h 257 0x7ff6a7778c92 30 QtPrivate::QFunctorSlotObject<<lambda_98a6b26bf0d27f8737cd826cc5a9a62a>,0,QtPrivate::List<>,void>::impl qobjectdefs_impl.h 449 0x7ff6a777ce87 31 QtPrivate::QSlotObjectBase::call qobjectdefs_impl.h 398 0x7ffe3daccd22 32 doActivate<0> qobject.cpp 3870 0x7ffe3db2548c 33 QMetaObject::activate qobject.cpp 3931 0x7ffe3db12d77 34 QAbstractButton::clicked moc_qabstractbutton.cpp 314 0x7ffe3f541e02 35 QAbstractButtonPrivate::emitClicked qabstractbutton.cpp 417 0x7ffe3f544054 36 QAbstractButtonPrivate::click qabstractbutton.cpp 409 0x7ffe3f543024 37 QAbstractButton::mouseReleaseEvent qabstractbutton.cpp 1013 0x7ffe3f5425f1 38 QToolButton::mouseReleaseEvent qtoolbutton.cpp 623 0x7ffe3f7105dc 39 QWidget::event qwidget.cpp 8660 0x7ffe3f3c4fcf 40 QAbstractButton::event qabstractbutton.cpp 970 0x7ffe3f542052 41 QToolButton::event qtoolbutton.cpp 1003 0x7ffe3f710424 42 QApplicationPrivate::notify_helper qapplication.cpp 3685 0x7ffe3f362c4f 43 QApplication::notify qapplication.cpp 3129 0x7ffe3f35d6f4 44 QCoreApplication::notifyInternal2 qcoreapplication.cpp 1075 0x7ffe3dab2aa0 45 QCoreApplication::sendSpontaneousEvent qcoreapplication.cpp 1483 0x7ffe3dab293b 46 QApplicationPrivate::sendMouseEvent qapplication.cpp 2615 0x7ffe3f3656c2 47 QWidgetWindow::handleMouseEvent qwidgetwindow.cpp 675 0x7ffe3f417b18 48 QWidgetWindow::event qwidgetwindow.cpp 296 0x7ffe3f415e31 49 QApplicationPrivate::notify_helper qapplication.cpp 3685 0x7ffe3f362c4f 50 QApplication::notify qapplication.cpp 3025 0x7ffe3f35ce07 51 QCoreApplication::notifyInternal2 qcoreapplication.cpp 1075 0x7ffe3dab2aa0 52 QCoreApplication::sendSpontaneousEvent qcoreapplication.cpp 1483 0x7ffe3dab293b 53 QGuiApplicationPrivate::processMouseEvent qguiapplication.cpp 2204 0x7ffe3e3b6b64 54 QGuiApplicationPrivate::processWindowSystemEvent qguiapplication.cpp 1936 0x7ffe3e3ba116 55 QWindowSystemInterface::sendWindowSystemEvents qwindowsysteminterface.cpp 1176 0x7ffe3e384602 56 QWindowsGuiEventDispatcher::sendPostedEvents qwindowsguieventdispatcher.cpp 83 0x7ffe36c867d2 57 QEventDispatcherWin32::processEvents qeventdispatcher_win.cpp 525 0x7ffe3db84b6e 58 QWindowsGuiEventDispatcher::processEvents qwindowsguieventdispatcher.cpp 74 0x7ffe36c86784 59 QEventLoop::processEvents qeventloop.cpp 139 0x7ffe3daad1cd 60 QEventLoop::exec qeventloop.cpp 225 0x7ffe3daad41f 61 QDialog::exec qdialog.cpp 602 0x7ffe3f744eff 62 MainWindow::onConvertirShapes MenuHerramientas.cpp 31 0x7ff6a7839546 63 QtPrivate::FunctorCall<QtPrivate::IndexesList<>,QtPrivate::List<>,void,void (__cdecl MainWindow:: *)(void)>::call qobjectdefs_impl.h 152 0x7ff6a78151eb 64 QtPrivate::FunctionPointer<void (__cdecl MainWindow:: *)(void)>::call<QtPrivate::List<>,void> qobjectdefs_impl.h 186 0x7ff6a780b8ad 65 QtPrivate::QSlotObject<void (__cdecl MainWindow:: *)(void),QtPrivate::List<>,void>::impl qobjectdefs_impl.h 419 0x7ff6a7816ccd 66 QtPrivate::QSlotObjectBase::call qobjectdefs_impl.h 398 0x7ffe3daccd22 67 doActivate<0> qobject.cpp 3870 0x7ffe3db2548c 68 QMetaObject::activate qobject.cpp 3931 0x7ffe3db12d77 69 QAction::triggered moc_qaction.cpp 382 0x7ffe3f338232 70 QAction::activate qaction.cpp 1162 0x7ffe3f337549 71 QMenuPrivate::activateCausedStack qmenu.cpp 1355 0x7ffe3f65b7c3 72 QMenuPrivate::activateAction qmenu.cpp 1433 0x7ffe3f65b6a4 73 QMenu::mouseReleaseEvent qmenu.cpp 2911 0x7ffe3f6522e0 74 QWidget::event qwidget.cpp 8660 0x7ffe3f3c4fcf 75 QMenu::event qmenu.cpp 3033 0x7ffe3f654b29 76 QApplicationPrivate::notify_helper qapplication.cpp 3685 0x7ffe3f362c4f 77 QApplication::notify qapplication.cpp 3129 0x7ffe3f35d6f4 78 QCoreApplication::notifyInternal2 qcoreapplication.cpp 1075 0x7ffe3dab2aa0 79 QCoreApplication::sendSpontaneousEvent qcoreapplication.cpp 1483 0x7ffe3dab293b 80 QApplicationPrivate::sendMouseEvent qapplication.cpp 2615 0x7ffe3f3656c2 81 QWidgetWindow::handleMouseEvent qwidgetwindow.cpp 573 0x7ffe3f416ed8 82 QWidgetWindow::event qwidgetwindow.cpp 296 0x7ffe3f415e31 83 QApplicationPrivate::notify_helper qapplication.cpp 3685 0x7ffe3f362c4f 84 QApplication::notify qapplication.cpp 3025 0x7ffe3f35ce07 85 QCoreApplication::notifyInternal2 qcoreapplication.cpp 1075 0x7ffe3dab2aa0 86 QCoreApplication::sendSpontaneousEvent qcoreapplication.cpp 1483 0x7ffe3dab293b 87 QGuiApplicationPrivate::processMouseEvent qguiapplication.cpp 2204 0x7ffe3e3b6b64 88 QGuiApplicationPrivate::processWindowSystemEvent qguiapplication.cpp 1936 0x7ffe3e3ba116 89 QWindowSystemInterface::sendWindowSystemEvents qwindowsysteminterface.cpp 1176 0x7ffe3e384602 90 QWindowsGuiEventDispatcher::sendPostedEvents qwindowsguieventdispatcher.cpp 83 0x7ffe36c867d2 91 QEventDispatcherWin32::processEvents qeventdispatcher_win.cpp 525 0x7ffe3db84b6e 92 QWindowsGuiEventDispatcher::processEvents qwindowsguieventdispatcher.cpp 74 0x7ffe36c86784 93 QEventLoop::processEvents qeventloop.cpp 139 0x7ffe3daad1cd 94 QEventLoop::exec qeventloop.cpp 225 0x7ffe3daad41f 95 QCoreApplication::exec qcoreapplication.cpp 1383 0x7ffe3dab076a 96 QGuiApplication::exec qguiapplication.cpp 1861 0x7ffe3e3b2aa8 97 QApplication::exec qapplication.cpp 2826 0x7ffe3f35c71a 98 main main.cpp 148 0x7ff6a7587089 99 WinMain qtmain_win.cpp 97 0x7ff6a7910c05 100 invoke_main exe_common.inl 107 0x7ff6a790f23d 101 __scrt_common_main_seh exe_common.inl 288 0x7ff6a790f12e 102 __scrt_common_main exe_common.inl 331 0x7ff6a790efee 103 WinMainCRTStartup exe_winmain.cpp 17 0x7ff6a790f2c9 104 BaseThreadInitThunk KERNEL32 0x7fff010e7614 105 RtlUserThreadStart ntdll 0x7fff02c026a1MenuHerramientas.cpp, starting in line 29:
void MainWindow::onConvertirShapes() { DlgShp2Tif dlgShp2Tif(this); if (dlgShp2Tif.exec() == QDialog::Accepted) { QString strShape, strImage; uint fieldNo; QString ficheroModelos; crs::CoordinateSystem crsIn, crsOut; double pixelYSize, pixelXSize; dlgShp2Tif.values(strShape, fieldNo, crsIn, ficheroModelos, pixelXSize, pixelYSize, crsOut, strImage); QString nombreShape, nombreImagen, extension; splitPath(strShape, nombreShape, extension); splitPath(strImage, nombreImagen, extension);And the lambda function:
connect(ui->btnShape, &QToolButton::clicked, this, [=]() { QString nombre = QFileDialog::getOpenFileName(this, tr("Seleccione fichero Shape"), s_shape, tr("Ficheros shape (*.shp)"), nullptr, QFileDialog::ReadOnly); if (!nombre.isEmpty()) { ui->shape->setText(nombre); } });I have put the breakpoint on the destructor, and as expected, it has not been invoked.
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Finally, it has fixed the problem, although I still do not know the cause. I deleted the build directories of both the application and the shared library, reconfigured the project, and build everything. As a result, it works again.
Many thanks to those who have tried to help me.
