Interesting little Segfault w/r to signal/slot connection

[Hydragyrum]

Good Afternoon

I've got an interesting little segfault that I can't seem to figure out why it's happening.

This is using Qt 4.1.0 I beleive.

First of all, here's a dump of the backtrace:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread -150056832 (LWP 3712)]
0x00f14c67 in QObject::connect (sender=0x8461ea0, signal=0x805c630 "2currentItemChanged( QTableWidgetItem *, QTableWidgetItem * )", receiver=0x83f3688,
method=0x805c5fc "1validate( QTableWidgetItem *, QTableWidgetItem * )", type=AutoConnection) at kernel/qobject.cpp:2134
2134 kernel/qobject.cpp: No such file or directory.
in kernel/qobject.cpp
(gdb) bt
#0 0x00f14c67 in QObject::connect (sender=0x8461ea0, signal=0x805c630 "2currentItemChanged( QTableWidgetItem *, QTableWidgetItem * )", receiver=0x83f3688,
method=0x805c5fc "1validate( QTableWidgetItem *, QTableWidgetItem * )", type=AutoConnection) at kernel/qobject.cpp:2134
#1 0x080563a4 in DataGen::setUpConnections (this=0x83f3688) at datagen.cpp:553
#2 0x0804d480 in DataGen (this=0x83f3688) at datagen.cpp:45
#3 0x08057d73 in main (argc=1, argv=0xfef1b434) at main.cpp:12

At first glance, it seems that the signal slot connection is having a hard time being made. The file not found error seems to point to something wrong with the Qt install, but here's the kicker, the exact same code runs perfectly fine in another project I have, on the same machine no less. So I'm not sure that the Qt install is the problem.

The code that seems to be closest to causing this fault is in the setUpConnections function, relevent snippet is here:

void DataGen::setUpConnections()
{
	//Signals and Slot Connections.
	//This line is causing the problem, although it's syntactically and semantically correct...at least it seems to be.
	connect( m_munPhRanges, SIGNAL( currentItemChanged( QTableWidgetItem *, QTableWidgetItem * ) ),
		this, SLOT( validate( QTableWidgetItem *, QTableWidgetItem * ) ) );
	connect( m_munPkRanges, SIGNAL( currentItemChanged( QTableWidgetItem *, QTableWidgetItem * ) ),
		this, SLOT( validate( QTableWidgetItem *, QTableWidgetItem * ) ) );
...
}

void DataGen::setUpConnections()
{
	//Signals and Slot Connections.
	//This line is causing the problem, although it's syntactically and semantically correct...at least it seems to be.
	connect( m_munPhRanges, SIGNAL( currentItemChanged( QTableWidgetItem *, QTableWidgetItem * ) ),
		this, SLOT( validate( QTableWidgetItem *, QTableWidgetItem * ) ) );
	connect( m_munPkRanges, SIGNAL( currentItemChanged( QTableWidgetItem *, QTableWidgetItem * ) ),
		this, SLOT( validate( QTableWidgetItem *, QTableWidgetItem * ) ) );
...
}

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The validate function prototype is as follows:

/**
 * @brief Slot used to validate the entries in a table. Called when a cell is finished editing,
 *    will turn the cell background red in the event of an invalid input. Values inported from file are assumed to be correct.
 * @param current Pointer to the TableWidgetItem in the current cell (not used, required by the signal).
 * @param previous Pointer to the previously edited TableWidgetItem.
 */
void validate(  QTableWidgetItem * current, QTableWidgetItem * previous );

/**
 * @brief Slot used to validate the entries in a table. Called when a cell is finished editing,
 *    will turn the cell background red in the event of an invalid input. Values inported from file are assumed to be correct.
 * @param current Pointer to the TableWidgetItem in the current cell (not used, required by the signal).
 * @param previous Pointer to the previously edited TableWidgetItem.
 */
void validate(  QTableWidgetItem * current, QTableWidgetItem * previous );

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If there's anything else you guys need, I'll try to see what I can do.

Thanks.

[jacek]

Are m_munPhRanges and m_munPkRanges initialized? Can you post the code that does this?

[Hydragyrum]

yeah they are

//Set up tables
	m_munPhRanges = new QTableWidget();
	m_munPhRanges -> setRowCount( 3 );
	m_munPhRanges -> setColumnCount( m_numRangesPh );
	m_munPhRanges -> setHorizontalHeaderLabels( rgePhHeadH );
	m_munPhRanges -> setVerticalHeaderLabels( rgePhHeadV );
	m_munPhRanges -> setFixedSize( 635, 110 );
	m_munPhRanges -> setRowHeight( 0, 20 );
	m_munPhRanges -> setRowHeight( 1, 20 );
	m_munPhRanges -> setRowHeight( 2, 20 );
 
	m_munPkRanges = new QTableWidget();
	m_munPkRanges -> setRowCount( 2 );
	m_munPkRanges -> setColumnCount( m_numRangesPk );
	m_munPkRanges -> setHorizontalHeaderLabels( rgePkHeadH );
	m_munPkRanges -> setVerticalHeaderLabels( rgePkHeadV );
	m_munPkRanges -> setFixedSize( 640, 90 );
	m_munPkRanges -> setRowHeight( 0, 20 );
	m_munPkRanges -> setRowHeight( 1, 20 );

//Set up tables
	m_munPhRanges = new QTableWidget();
	m_munPhRanges -> setRowCount( 3 );
	m_munPhRanges -> setColumnCount( m_numRangesPh );
	m_munPhRanges -> setHorizontalHeaderLabels( rgePhHeadH );
	m_munPhRanges -> setVerticalHeaderLabels( rgePhHeadV );
	m_munPhRanges -> setFixedSize( 635, 110 );
	m_munPhRanges -> setRowHeight( 0, 20 );
	m_munPhRanges -> setRowHeight( 1, 20 );
	m_munPhRanges -> setRowHeight( 2, 20 );
	
	m_munPkRanges = new QTableWidget();
	m_munPkRanges -> setRowCount( 2 );
	m_munPkRanges -> setColumnCount( m_numRangesPk );
	m_munPkRanges -> setHorizontalHeaderLabels( rgePkHeadH );
	m_munPkRanges -> setVerticalHeaderLabels( rgePkHeadV );
	m_munPkRanges -> setFixedSize( 640, 90 );
	m_munPkRanges -> setRowHeight( 0, 20 );
	m_munPkRanges -> setRowHeight( 1, 20 );

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Everything compiles correctly. The things are also in the class definition in the header.

As mentioned earlier, I have the exact same setup in a different project (basically rewriting this one to do the same thing, only better) and that one works fine.

[jacek]

Where is this code placed? Are you sure that it's executed before setUpConnections()?

[Hydragyrum]

yeah, that code is in the setUpWidgets function, which due to it's length, I will not post here. I will post the constructor though...

DataGen::DataGen()
{
	//We'll set a default value for number of munition ranges to 5. doesn't matter really.
	m_numRangesPh = m_numRangesPk = 5;
 
	//Set up the widgets.
	setUpWidgets();
 
	m_dataFile = "";
	m_dataDir = QCoreApplication::applicationDirPath ();
 
	//Set up the signal/slot connections.
	setUpConnections();
 
	//Let the selector equal nothing;
	m_selector -> setCurrentIndex(-1);
 
	//Let the Munition type be nothing by default
	m_munType -> setCurrentIndex(-1);
 
	//Initialize tables.
	initTgtTables();
	initMunTables();
 
	setWindowFlags ( Qt::WindowMinMaxButtonsHint );
}

DataGen::DataGen()
{
	//We'll set a default value for number of munition ranges to 5. doesn't matter really.
	m_numRangesPh = m_numRangesPk = 5;

	//Set up the widgets.
	setUpWidgets();

	m_dataFile = "";
	m_dataDir = QCoreApplication::applicationDirPath ();
	
	//Set up the signal/slot connections.
	setUpConnections();
	
	//Let the selector equal nothing;
	m_selector -> setCurrentIndex(-1);
	
	//Let the Munition type be nothing by default
	m_munType -> setCurrentIndex(-1);

	//Initialize tables.
	initTgtTables();
	initMunTables();

	setWindowFlags ( Qt::WindowMinMaxButtonsHint );
}

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[jacek]

Does setUpWidgets() happen to be a virtual method?

[Hydragyrum]

Does setUpWidgets() happen to be a virtual method?

Nope, it's not virtual.

To me, it doesn't quite look like a code problem, nor an install issue, since it works on another project...I really don't know what else it could be...

[jacek]

Add:

DataGen::DataGen() : m_munPhRanges( 0xdeadbeef ), m_munPkRanges( 0xcafebabe )
{
   ...

DataGen::DataGen() : m_munPhRanges( 0xdeadbeef ), m_munPkRanges( 0xcafebabe )
{
   ...

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and check the stack trace (just to make sure that these variables are initialized).

Do you create QApplication instance at the beginning of main()? Also check with ldd which Qt library your program is linked with.

[Hydragyrum]

ldd is reporting that everything should be fine, here's the dump

linux-gate.so.1 =>  (0x00c87000)
        libQtGui_debug.so.4 => /usr/local/Trolltech/Qt-4.1.0/lib/libQtGui_debug.so.4 (0x00111000)
        libpng12.so.0 => /usr/lib/libpng12.so.0 (0x07afc000)
        libSM.so.6 => /usr/X11R6/lib/libSM.so.6 (0x00de0000)
        libICE.so.6 => /usr/X11R6/lib/libICE.so.6 (0x00d48000)
        libXi.so.6 => /usr/X11R6/lib/libXi.so.6 (0x0080e000)
        libXrender.so.1 => /usr/X11R6/lib/libXrender.so.1 (0x00816000)
        libXrandr.so.2 => /usr/X11R6/lib/libXrandr.so.2 (0x0081e000)
        libXcursor.so.1 => /usr/X11R6/lib/libXcursor.so.1 (0x00821000)
        libXinerama.so.1 => /usr/X11R6/lib/libXinerama.so.1 (0x07888000)
        libfreetype.so.6 => /usr/lib/libfreetype.so.6 (0x0082a000)
        libfontconfig.so.1 => /usr/lib/libfontconfig.so.1 (0x0088f000)
        libXext.so.6 => /usr/X11R6/lib/libXext.so.6 (0x00d25000)
        libX11.so.6 => /usr/X11R6/lib/libX11.so.6 (0x008b6000)
        libQtCore_debug.so.4 => /usr/local/Trolltech/Qt-4.1.0/lib/libQtCore_debug.so.4 (0x00de8000)
        libz.so.1 => /usr/lib/libz.so.1 (0x00d35000)
        libdl.so.2 => /lib/libdl.so.2 (0x00c55000)
        libpthread.so.0 => /lib/tls/libpthread.so.0 (0x0097e000)
        libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x07728000)
        libm.so.6 => /lib/tls/libm.so.6 (0x00c30000)
        libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x00a5a000)
        libc.so.6 => /lib/tls/libc.so.6 (0x00b13000)
        libexpat.so.0 => /usr/lib/libexpat.so.0 (0x00990000)
        /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00afa000)

linux-gate.so.1 =>  (0x00c87000)
        libQtGui_debug.so.4 => /usr/local/Trolltech/Qt-4.1.0/lib/libQtGui_debug.so.4 (0x00111000)
        libpng12.so.0 => /usr/lib/libpng12.so.0 (0x07afc000)
        libSM.so.6 => /usr/X11R6/lib/libSM.so.6 (0x00de0000)
        libICE.so.6 => /usr/X11R6/lib/libICE.so.6 (0x00d48000)
        libXi.so.6 => /usr/X11R6/lib/libXi.so.6 (0x0080e000)
        libXrender.so.1 => /usr/X11R6/lib/libXrender.so.1 (0x00816000)
        libXrandr.so.2 => /usr/X11R6/lib/libXrandr.so.2 (0x0081e000)
        libXcursor.so.1 => /usr/X11R6/lib/libXcursor.so.1 (0x00821000)
        libXinerama.so.1 => /usr/X11R6/lib/libXinerama.so.1 (0x07888000)
        libfreetype.so.6 => /usr/lib/libfreetype.so.6 (0x0082a000)
        libfontconfig.so.1 => /usr/lib/libfontconfig.so.1 (0x0088f000)
        libXext.so.6 => /usr/X11R6/lib/libXext.so.6 (0x00d25000)
        libX11.so.6 => /usr/X11R6/lib/libX11.so.6 (0x008b6000)
        libQtCore_debug.so.4 => /usr/local/Trolltech/Qt-4.1.0/lib/libQtCore_debug.so.4 (0x00de8000)
        libz.so.1 => /usr/lib/libz.so.1 (0x00d35000)
        libdl.so.2 => /lib/libdl.so.2 (0x00c55000)
        libpthread.so.0 => /lib/tls/libpthread.so.0 (0x0097e000)
        libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x07728000)
        libm.so.6 => /lib/tls/libm.so.6 (0x00c30000)
        libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x00a5a000)
        libc.so.6 => /lib/tls/libc.so.6 (0x00b13000)
        libexpat.so.0 => /usr/lib/libexpat.so.0 (0x00990000)
        /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x00afa000)

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I know that these locations all exist.

As for the initialization thing it's throwing out compile errors about an invalid conversion

datagen.cpp: In constructor `DataGen::DataGen()':
datagen.cpp:34: error: invalid conversion from `unsigned int' to `QTableWidget*
   '
datagen.cpp:34: error: invalid conversion from `unsigned int' to `QTableWidget*
   '

datagen.cpp: In constructor `DataGen::DataGen()':
datagen.cpp:34: error: invalid conversion from `unsigned int' to `QTableWidget*
   '
datagen.cpp:34: error: invalid conversion from `unsigned int' to `QTableWidget*
   '

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Trying to solve that problem right now.

Edit: The QTableWidget pointer doesn't seem to want to let me initialize it's address to a random memory location...

[Hydragyrum]

Another interesting development, my constructor isn't even called...I set a breakpoint at the start of my constructor, and I get the same error, ie the segfault.

although at least main is being called

the segfault occurs when trying to initialize my primary class.

GDB dump follows:

12 DataGen * d = new DataGen();
(gdb)
Error while reading shared library symbols:
: No such file or directory.
Error while reading shared library symbols:
: No such file or directory.
Error while reading shared library symbols:
: No such file or directory.
Error while reading shared library symbols:
: No such file or directory.

Program received signal SIGSEGV, Segmentation fault.
0x00f14c67 in QObject::connect (sender=0x816cea0, signal=0x805c630 "2currentItemChanged( QTableWidgetItem *, QTableWidgetItem * )", receiver=0x80fe688,
method=0x805c5fc "1validate( QTableWidgetItem *, QTableWidgetItem * )", type=AutoConnection) at kernel/qobject.cpp:2134
2134 kernel/qobject.cpp: No such file or directory.
in kernel/qobject.cpp

I should clarify, I have a couple breakpoints set to the start of my default constructor, and the start of the main function. using next, I went along until it segfaulted. Had the constructor been called, I'd have hit the breakpoint at the constructor.

[jacek]

/usr/local/Trolltech/Qt-4.1.0/lib/libQtGui_debug.so.4
/usr/local/Trolltech/Qt-4.1.0/lib/libQtCore_debug.so.4

Is that the only Qt4 version you have on your system?

datagen.cpp:34: error: invalid conversion from `unsigned int' to `QTableWidget*

I forgot to add casts:

DataGen::DataGen() : m_munPhRanges( (QTableWidget*)0xdeadbeef ), m_munPkRanges( (QTableWidget*)0xcafebabe )

DataGen::DataGen() : m_munPhRanges( (QTableWidget*)0xdeadbeef ), m_munPkRanges( (QTableWidget*)0xcafebabe )

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When it crashes just check whether these adresses are different.

Do you do anything else (except for initialization and connections) with m_munPhRanges and m_munPkRanges? Maybe you delete them by accident?

[Hydragyrum]

pretty sure I don't delete them, let Qt take care of that when the class gets nuked.

As far as I know, that's the only Qt4 version that exists on this machine.

the tables are not even declared yet at the point of the crash, since the constructor isn't even called...but it's somehow entering the setUpConnections function, which is only called from within the constructor...and I'm not sure why...

all optimization flags are off, btw.