QT4.2 corrupted double-linked list and QRadioButton existance

[jacek]

It also mentions that it is defined in <cstddef>.

Exactly, as I said, it's only for compatibility with C. In the new C++ standard, there will be a nullptr constant, but for now the first paragraph in section 4.10 says: "A null pointer constant is an integral constant expression (5.19) rvalue of integer type that evaluates to zero."

I couldn't see any logical reason why the function call should transform '0' into '0x6' unless it was an compiler "implementation" gotcha.

It could be, but 0 is used as a null pointer in many places in Qt sources, so it shouldn't be a problem.

I'd always prefer NULL over 0 but thats because I think its more readable, but there seems to be many opinions on this matter.

It also causes some problems with templates.

I don't remember seeing the class QIconvCodec in the public API

Neither did I. You can learn new things about Qt every day.

[mtrpoland]

Being desperate I decided to check whether the flawless QLabel evokes the problem and now I dare say I was trounced.
Why with two QLabels I receive an error and with one all is ok????

Here you have backtrace at 21:59 LT:

(gdb) backtrace
#0  0xffffe410 in __kernel_vsyscall ()
#1  0xb72c4770 in raise () from /lib/tls/i686/cmov/libc.so.6
#2  0xb72c5ef3 in abort () from /lib/tls/i686/cmov/libc.so.6
#3  0xb72f9d0b in __fsetlocking () from /lib/tls/i686/cmov/libc.so.6
#4  0xb73018bd in mallopt () from /lib/tls/i686/cmov/libc.so.6
#5  0xb7301a44 in free () from /lib/tls/i686/cmov/libc.so.6
#6  0xb75f0e5d in QHashData::freeNode (this=0x8112498, node=0x8124af8)
    at tools/qhash.cpp:132
#7  0xb7a4babd in QHash<unsigned long, QWidget*>::remove (this=0x8108d30,
    akey=@0x812498c)
    at ../../include/QtCore/../../src/corelib/tools/qhash.h:450
#8  0xb7a3ceff in QWidgetPrivate::setWinId (this=0x8124950, id=0)
    at kernel/qwidget.cpp:1180
#9  0xb7a72dcc in QWidget::destroy (this=0x81248b8, destroyWindow=true,
    destroySubWindows=true) at kernel/qwidget_x11.cpp:782
#10 0xb7a4266c in ~QWidget (this=0x81248b8) at kernel/qwidget.cpp:1162
#11 0xb7c91ef1 in ~QAbstractButton (this=0x81248b8)
    at widgets/qabstractbutton.cpp:572
#12 0xb7d3e6e5 in ~QToolButton (this=0x81248b8) at widgets/qtoolbutton.cpp:347
#13 0xb768eea1 in QObjectPrivate::deleteChildren (this=0x8123978)
    at kernel/qobject.cpp:1823
#14 0xb7a42649 in ~QWidget (this=0x8123938) at kernel/qwidget.cpp:1158
#15 0xb7d38844 in ~QToolBar (this=0x8123938) at widgets/qtoolbar.cpp:472
---Type <return> to continue, or q <return> to quit---
#16 0xb768eea1 in QObjectPrivate::deleteChildren (this=0x810b300)
    at kernel/qobject.cpp:1823
#17 0xb7a42649 in ~QWidget (this=0xbfec0a50) at kernel/qwidget.cpp:1158
#18 0xb7ceac21 in ~QMainWindow (this=0xbfec0a50) at widgets/qmainwindow.cpp:292
#19 0x080527ca in main ()

(gdb) backtrace
#0  0xffffe410 in __kernel_vsyscall ()
#1  0xb72c4770 in raise () from /lib/tls/i686/cmov/libc.so.6
#2  0xb72c5ef3 in abort () from /lib/tls/i686/cmov/libc.so.6
#3  0xb72f9d0b in __fsetlocking () from /lib/tls/i686/cmov/libc.so.6
#4  0xb73018bd in mallopt () from /lib/tls/i686/cmov/libc.so.6
#5  0xb7301a44 in free () from /lib/tls/i686/cmov/libc.so.6
#6  0xb75f0e5d in QHashData::freeNode (this=0x8112498, node=0x8124af8)
    at tools/qhash.cpp:132
#7  0xb7a4babd in QHash<unsigned long, QWidget*>::remove (this=0x8108d30,
    akey=@0x812498c)
    at ../../include/QtCore/../../src/corelib/tools/qhash.h:450
#8  0xb7a3ceff in QWidgetPrivate::setWinId (this=0x8124950, id=0)
    at kernel/qwidget.cpp:1180
#9  0xb7a72dcc in QWidget::destroy (this=0x81248b8, destroyWindow=true,
    destroySubWindows=true) at kernel/qwidget_x11.cpp:782
#10 0xb7a4266c in ~QWidget (this=0x81248b8) at kernel/qwidget.cpp:1162
#11 0xb7c91ef1 in ~QAbstractButton (this=0x81248b8)
    at widgets/qabstractbutton.cpp:572
#12 0xb7d3e6e5 in ~QToolButton (this=0x81248b8) at widgets/qtoolbutton.cpp:347
#13 0xb768eea1 in QObjectPrivate::deleteChildren (this=0x8123978)
    at kernel/qobject.cpp:1823
#14 0xb7a42649 in ~QWidget (this=0x8123938) at kernel/qwidget.cpp:1158
#15 0xb7d38844 in ~QToolBar (this=0x8123938) at widgets/qtoolbar.cpp:472
---Type <return> to continue, or q <return> to quit---
#16 0xb768eea1 in QObjectPrivate::deleteChildren (this=0x810b300)
    at kernel/qobject.cpp:1823
#17 0xb7a42649 in ~QWidget (this=0xbfec0a50) at kernel/qwidget.cpp:1158
#18 0xb7ceac21 in ~QMainWindow (this=0xbfec0a50) at widgets/qmainwindow.cpp:292
#19 0x080527ca in main ()

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and at 22:00 LT

(gdb) backtrace
#0  0xffffe410 in __kernel_vsyscall ()
#1  0xb71f3770 in raise () from /lib/tls/i686/cmov/libc.so.6
#2  0xb71f4ef3 in abort () from /lib/tls/i686/cmov/libc.so.6
#3  0xb7228d0b in __fsetlocking () from /lib/tls/i686/cmov/libc.so.6
#4  0xb72308bd in mallopt () from /lib/tls/i686/cmov/libc.so.6
#5  0xb7230a44 in free () from /lib/tls/i686/cmov/libc.so.6
#6  0xb751fe5d in QHashData::freeNode (this=0x8112498, node=0x8124af8)
    at tools/qhash.cpp:132
#7  0xb797aabd in QHash<unsigned long, QWidget*>::remove (this=0x8108d30,
    akey=@0x812498c)
    at ../../include/QtCore/../../src/corelib/tools/qhash.h:450
#8  0xb796beff in QWidgetPrivate::setWinId (this=0x8124950, id=0)
    at kernel/qwidget.cpp:1180
#9  0xb79a1dcc in QWidget::destroy (this=0x81248b8, destroyWindow=true,
    destroySubWindows=true) at kernel/qwidget_x11.cpp:782
#10 0xb797166c in ~QWidget (this=0x81248b8) at kernel/qwidget.cpp:1162
#11 0xb7bc0ef1 in ~QAbstractButton (this=0x81248b8)
    at widgets/qabstractbutton.cpp:572
#12 0xb7c6d6e5 in ~QToolButton (this=0x81248b8) at widgets/qtoolbutton.cpp:347
#13 0xb75bdea1 in QObjectPrivate::deleteChildren (this=0x8123978)
    at kernel/qobject.cpp:1823
#14 0xb7971649 in ~QWidget (this=0x8123938) at kernel/qwidget.cpp:1158
#15 0xb7c67844 in ~QToolBar (this=0x8123938) at widgets/qtoolbar.cpp:472
---Type <return> to continue, or q <return> to quit---
#16 0xb75bdea1 in QObjectPrivate::deleteChildren (this=0x810b300)
    at kernel/qobject.cpp:1823
#17 0xb7971649 in ~QWidget (this=0xbf9e0d70) at kernel/qwidget.cpp:1158
#18 0xb7c19c21 in ~QMainWindow (this=0xbf9e0d70) at widgets/qmainwindow.cpp:292
#19 0x080527ca in main ()

(gdb) backtrace
#0  0xffffe410 in __kernel_vsyscall ()
#1  0xb71f3770 in raise () from /lib/tls/i686/cmov/libc.so.6
#2  0xb71f4ef3 in abort () from /lib/tls/i686/cmov/libc.so.6
#3  0xb7228d0b in __fsetlocking () from /lib/tls/i686/cmov/libc.so.6
#4  0xb72308bd in mallopt () from /lib/tls/i686/cmov/libc.so.6
#5  0xb7230a44 in free () from /lib/tls/i686/cmov/libc.so.6
#6  0xb751fe5d in QHashData::freeNode (this=0x8112498, node=0x8124af8)
    at tools/qhash.cpp:132
#7  0xb797aabd in QHash<unsigned long, QWidget*>::remove (this=0x8108d30,
    akey=@0x812498c)
    at ../../include/QtCore/../../src/corelib/tools/qhash.h:450
#8  0xb796beff in QWidgetPrivate::setWinId (this=0x8124950, id=0)
    at kernel/qwidget.cpp:1180
#9  0xb79a1dcc in QWidget::destroy (this=0x81248b8, destroyWindow=true,
    destroySubWindows=true) at kernel/qwidget_x11.cpp:782
#10 0xb797166c in ~QWidget (this=0x81248b8) at kernel/qwidget.cpp:1162
#11 0xb7bc0ef1 in ~QAbstractButton (this=0x81248b8)
    at widgets/qabstractbutton.cpp:572
#12 0xb7c6d6e5 in ~QToolButton (this=0x81248b8) at widgets/qtoolbutton.cpp:347
#13 0xb75bdea1 in QObjectPrivate::deleteChildren (this=0x8123978)
    at kernel/qobject.cpp:1823
#14 0xb7971649 in ~QWidget (this=0x8123938) at kernel/qwidget.cpp:1158
#15 0xb7c67844 in ~QToolBar (this=0x8123938) at widgets/qtoolbar.cpp:472
---Type <return> to continue, or q <return> to quit---
#16 0xb75bdea1 in QObjectPrivate::deleteChildren (this=0x810b300)
    at kernel/qobject.cpp:1823
#17 0xb7971649 in ~QWidget (this=0xbf9e0d70) at kernel/qwidget.cpp:1158
#18 0xb7c19c21 in ~QMainWindow (this=0xbf9e0d70) at widgets/qmainwindow.cpp:292
#19 0x080527ca in main ()

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And finally here you have two complete listings...
mymvc.h

#ifndef MTR_SAFETY_DECLARATION_FOR_MYMVC_H
#define MTR_SAFETY_DECLARATION_FOR_MYMVC_H
#include <QWidget>
namespace MTR {
class Book;
class SBook;
}
class myView;
class myModel;
class QVBoxLayout;
class QLabel;
class QComboBox;
class QLineEdit;
 
class MyMVC : public QWidget {
	Q_OBJECT
public:
	MyMVC(QList<MTR::Book>* list = 0, QWidget* parent = 0);
	void prodModel(QList<MTR::Book>*);
public slots:
	void setCaseSensitive(bool cs) { caseSensitive = cs; }
signals:
	void doubleClickInTreeView(int);
private:
	QList<MTR::SBook>* slist;
	QLineEdit* le;
	QComboBox* qcb;
	myModel* model;
	myView* qtv;
	QVBoxLayout* qvb;
	QLabel* label;
	QLabel* whatTheHell; //IF COMMENTED, DOES NOT CAUSE ERROR
	bool caseSensitive;
};
 
#endif

#ifndef MTR_SAFETY_DECLARATION_FOR_MYMVC_H
#define MTR_SAFETY_DECLARATION_FOR_MYMVC_H
#include <QWidget>
namespace MTR {
class Book;
class SBook;
}
class myView;
class myModel;
class QVBoxLayout;
class QLabel;
class QComboBox;
class QLineEdit;

class MyMVC : public QWidget {
	Q_OBJECT
public:
	MyMVC(QList<MTR::Book>* list = 0, QWidget* parent = 0);
	void prodModel(QList<MTR::Book>*);
public slots:
	void setCaseSensitive(bool cs) { caseSensitive = cs; }
signals:
	void doubleClickInTreeView(int);
private:
	QList<MTR::SBook>* slist;
	QLineEdit* le;
	QComboBox* qcb;
	myModel* model;
	myView* qtv;
	QVBoxLayout* qvb;
	QLabel* label;
	QLabel* whatTheHell; //IF COMMENTED, DOES NOT CAUSE ERROR
	bool caseSensitive;
};

#endif

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and mymvc.cpp

#include "mymvc.h"
#include "myView.h"
#include "sbook.h"
#include "myModel.h"
#include "myHeaderView.h"
#include <QList>
#include <QVBoxLayout>
#include <QLabel>
#include <QLineEdit>
#include <QComboBox>
#include <QCheckBox>
 
MyMVC::MyMVC(QList<MTR::Book>* list, QWidget* parent) {
	slist = new QList<MTR::SBook>();
	for(int i = 0;i<list->size();++i) {
		slist->append(MTR::SBook(i,list->value(i)));
	}
   setFixedSize(590,400);
 
   le = new QLineEdit();
   qcb = new QComboBox();
   qcb->addItem(tr("filter by Title"));
   qcb->addItem(tr("filter by Author"));
   qcb->addItem(tr("filter by Publisher"));
   qcb->setCurrentIndex(0);
 
   model = new myModel(*slist,le,qcb);
	model->filter();
 
   qtv = new myView(model);
	qtv->header()->setSortIndicator(0,Qt::DescendingOrder);
 
   label = new QLabel(tr("Enter a character string below"));
   whatTheHell = new QLabel(tr("Damn")); //IF COMMENTED, DOES NOT CAUSE ERROR
	caseSensitive = true;
   qvb = new QVBoxLayout();
   connect(qcb,SIGNAL(currentIndexChanged(int)),le,SLOT(clear()));
   connect(qcb,SIGNAL(currentIndexChanged(int)),qtv,SLOT(filter()));
   connect(le,SIGNAL(textChanged(const QString &)),qtv,SLOT(filter()));
   connect(model,SIGNAL(fromTVtoVM(int)),this,SIGNAL(doubleClickInTreeView(int)));
 
   qvb->addWidget(label);
   qvb->addWidget(le);
   qvb->addWidget(whatTheHell); //IF COMMENTED, DOES NOT CAUSE ERROR
   qvb->addWidget(qcb);
   qvb->addWidget(qtv);
   setLayout(qvb);
}
 
void MyMVC::prodModel(QList<MTR::Book>* list) {
	slist->clear();
	for(int i = 0;i<list->size();++i) {
		slist->append(MTR::SBook(i,list->value(i)));
	}
	model->setInternalList(*slist);
   qcb->setCurrentIndex(0);
	qtv->filter();
 
}

#include "mymvc.h"
#include "myView.h"
#include "sbook.h"
#include "myModel.h"
#include "myHeaderView.h"
#include <QList>
#include <QVBoxLayout>
#include <QLabel>
#include <QLineEdit>
#include <QComboBox>
#include <QCheckBox>

MyMVC::MyMVC(QList<MTR::Book>* list, QWidget* parent) {
	slist = new QList<MTR::SBook>();
	for(int i = 0;i<list->size();++i) {
		slist->append(MTR::SBook(i,list->value(i)));
	}
   setFixedSize(590,400);

   le = new QLineEdit();
   qcb = new QComboBox();
   qcb->addItem(tr("filter by Title"));
   qcb->addItem(tr("filter by Author"));
   qcb->addItem(tr("filter by Publisher"));
   qcb->setCurrentIndex(0);

   model = new myModel(*slist,le,qcb);
	model->filter();
	
   qtv = new myView(model);
	qtv->header()->setSortIndicator(0,Qt::DescendingOrder);

   label = new QLabel(tr("Enter a character string below"));
   whatTheHell = new QLabel(tr("Damn")); //IF COMMENTED, DOES NOT CAUSE ERROR
	caseSensitive = true;
   qvb = new QVBoxLayout();
   connect(qcb,SIGNAL(currentIndexChanged(int)),le,SLOT(clear()));
   connect(qcb,SIGNAL(currentIndexChanged(int)),qtv,SLOT(filter()));
   connect(le,SIGNAL(textChanged(const QString &)),qtv,SLOT(filter()));
   connect(model,SIGNAL(fromTVtoVM(int)),this,SIGNAL(doubleClickInTreeView(int)));

   qvb->addWidget(label);
   qvb->addWidget(le);
   qvb->addWidget(whatTheHell); //IF COMMENTED, DOES NOT CAUSE ERROR
   qvb->addWidget(qcb);
   qvb->addWidget(qtv);
   setLayout(qvb);
}

void MyMVC::prodModel(QList<MTR::Book>* list) {
	slist->clear();
	for(int i = 0;i<list->size();++i) {
		slist->append(MTR::SBook(i,list->value(i)));
	}
	model->setInternalList(*slist);
   qcb->setCurrentIndex(0);
	qtv->filter();

}

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[jacek]

How did you install Qt?

[jpn]

What does valgrind have to say about it?

[mtrpoland]

Valgrind?
I do not know whether it is useful as not long time ago I played with FlowLayout example (QT 4.2) and valgrind gave me:

==6237== LEAK SUMMARY:
==6237==    definitely lost: 88 bytes in 3 blocks.
==6237==    indirectly lost: 120 bytes in 10 blocks.
==6237==      possibly lost: 744 bytes in 3 blocks.
==6237==    still reachable: 322,563 bytes in 4,588 blocks.
==6237==         suppressed: 0 bytes in 0 blocks.

==6237== LEAK SUMMARY:
==6237==    definitely lost: 88 bytes in 3 blocks.
==6237==    indirectly lost: 120 bytes in 10 blocks.
==6237==      possibly lost: 744 bytes in 3 blocks.
==6237==    still reachable: 322,563 bytes in 4,588 blocks.
==6237==         suppressed: 0 bytes in 0 blocks.

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Now my 1600+ lines application gives me:

==6214== LEAK SUMMARY:
==6214==    definitely lost: 449 bytes in 32 blocks.
==6214==    indirectly lost: 1,526 bytes in 36 blocks.
==6214==      possibly lost: 744 bytes in 3 blocks.
==6214==    still reachable: 331,034 bytes in 4,629 blocks.
==6214==         suppressed: 0 bytes in 0 blocks.

==6214== LEAK SUMMARY:
==6214==    definitely lost: 449 bytes in 32 blocks.
==6214==    indirectly lost: 1,526 bytes in 36 blocks.
==6214==      possibly lost: 744 bytes in 3 blocks.
==6214==    still reachable: 331,034 bytes in 4,629 blocks.
==6214==         suppressed: 0 bytes in 0 blocks.

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So I suppose that some of those are because of qt libraries... Am I right?

Anyway, I may write some parts of valgrind message after checking my application.

[marcel]

I don't think this is getting anywhere.
If the app is only around 1600 lines, then why don't you post it here?
Would that be possible? Then someone could test it.

Regards

[mtrpoland]

Below are links to working application (I have circumvented the problem above) and package of code files and file containing some data to test program (one humble *.dat file).

Anyway, I would be glad if someone experienced checked some of my code for bugs and bad habits. I know it is difficult to ask you for such thing but marcel suggested such a solution himself.

The "funny" thing is when I de-comment code connected to QTranslator in main.cpp I get SIGSEV gift.
In other words I cannot translate my application using .ts file made by Linguist.

So my inference is that there is some crucial memory management bug in MY code that sometimes throws irrational SIGSEV, blocking me of using certain normal ways of programming.

I just cannot find it!

Program and code package in:
http://www.mjakobczyk.pl/pub/code/

[marcel]

I compiled your application( on Windows, Qt 4.3 ) but I cannot get it to crash( I uncommented the translator lines in main).
Could you say what steps are involved?

Regards

[jpn]

Here's at least one issue that prevents it from launching for me:

void MWin::initialization(void) {
	...
	tableViewWidget = new MyMVC(list); // list is yet uninitialized
	...
	list = new QList<MTR::Book>; // it's being initialized somewhere here afterwards
	...
}

void MWin::initialization(void) {
	...
	tableViewWidget = new MyMVC(list); // list is yet uninitialized
	...
	list = new QList<MTR::Book>; // it's being initialized somewhere here afterwards
	...
}

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I would suggest allocating QList objects on the stack and passing them as references. Allocating them on the heap is more error prone. QList is an implicitly shared class so unmodified copies are cheap.

[marcel]

Yeah, that and correct the following from:

namespace MTR {
class Book;
class SBook;
}

namespace MTR {
class Book;
class SBook;
}

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to:

namespace MTR {
class Book;
struct SBook;
}

namespace MTR {
class Book;
struct SBook;
}

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I was getting a few warnings and a linker error because of this.

Regards

[mtrpoland]

Gentlemen, now all indeed does work. A nod of respect. Thank you very much. Now I see that the key was what highlighted jpn. It destabilized my application.