C / C++ / MFC

31-Oct-02 13:38

I am really getting frustrated with this, so I finally decided to ask. If I leave the code highlighted red in, the application gets stuck in an infinite loop (I think), however if I take it out the application bombs. Does anyone have any suggestions/what might I be missing here? Thanks in advance. Smile | :)

int records::InsertNode(char m_last_name[], char m_first_name[], long m_ssan)
{
	ListNode *NewNode, *NodePtr, *PreviousNode;

	// Allocate a new node & store values
	NewNode = new ListNode;
	strcpy(NewNode->last_name, m_last_name);
	strcpy(NewNode->first_name, m_first_name);
	NewNode->ssan = m_ssan;
	
	// If there are no nodes in the list
	// make NewNode the first node
	if (!Head)
	{
		Head = NewNode;
		NewNode->Next = NULL;
	}
	else	// Otherwise, insert NewNode at end
	{
		// Initialize NodePtr to head of list
		NodePtr = Head;
		

		<font color="red">PreviousNode = NodePtr;</font>

		// Skip all nodes whose Value member is less
		// than m_ssan.

		while (NodePtr != NULL && NodePtr->ssan < m_ssan)
		{	
			PreviousNode = NodePtr;
			NodePtr = NodePtr->Next;
		}

		// Insert the node after the one pointed to
		// by PreviousNode and before the one pointed to
		// by NodePtr.
		PreviousNode->Next = NewNode;
		NewNode->Next = NodePtr;
	}
	return 0;
}

Nick Parker

May your glass be ever full.
May the roof over your head be always strong.
And may you be in heaven half an hour before the devil knows you’re dead. - Irish Blessing

Tim Smith31-Oct-02 13:51

Tim Smith

31-Oct-02 13:51

The problem is that if the second entry needs to become the new head, PreviousNode is still pointing to the next node and not the head.

I would initialize PN to NULL and then after the loop check if PN == NULL. If so, then treat as an insert at the head. Otherwise, treat normally.

Head Insert:

PN->Next really is NodePtr->Next. When you set that to NewNode and NewNode references NodePtr, you get your loop.

Tim Smith

I'm going to patent thought. I have yet to see any prior art.

Nick Parker31-Oct-02 14:06

31-Oct-02 14:06

Thanks Tim, I understood the top part, and while trying to implement it I think I #!*@ it up. This is what I added, is that what you are talking about (this still pukes)?

        NodePtr = Head;
        PreviousNode = NULL;
while (NodePtr != NULL && NodePtr->ssan < m_ssan)
{
    PreviousNode = NodePtr;
    NodePtr = NodePtr->Next;
}

if(PreviousNode== NULL)
{
    PreviousNode = NewNode;
    NewNode->Next = NodePtr;
}
else
{
    PreviousNode->Next = NewNode;
    NewNode->Next = NodePtr;
}

Nick Parker

May your glass be ever full.
May the roof over your head be always strong.
And may you be in heaven half an hour before the devil knows you’re dead. - Irish Blessing

ColinDavies31-Oct-02 14:11

ColinDavies

31-Oct-02 14:11

Unsure about Tim's answer yet.

but

if (!Head)
{
     Head = NewNode;
     NewNode->Next = NULL;
}

Why isn't PreviousNode given a default value here ?

Regardz
Colin J Davies

Sonork ID 100.9197:Colin

You are the intrepid one, always willing to leap into the fray! A serious character flaw, I might add, but entertaining.
Said by Roger Wright about me.

Nick Parker31-Oct-02 14:13

31-Oct-02 14:13

Colin Davies wrote:
if (!Head){ Head = NewNode; NewNode->Next = NULL;}

Why isn't PreviousNode given a default value here ?

PreviousNode isn't used if the Head isn't set yet, NewNode becomes the Head and then returns. Or did I miss something?

Nick Parker

May your glass be ever full.
May the roof over your head be always strong.
And may you be in heaven half an hour before the devil knows you’re dead. - Irish Blessing

Alexander Wiseman31-Oct-02 15:06

Alexander Wiseman

31-Oct-02 15:06

Hello!

Change your line in red to read:

<br />
PreviousNode = NULL;<br />

Then, below the while loop, add this code:

// Insert the node after the one pointed to
// by PreviousNode and before the one pointed to
// by NodePtr.
if(PreviousNode != NULL)
{
        PreviousNode->Next = NewNode;
        NewNode->Next = NodePtr;
}
else //new node becomes the first node
{
        NewNode->Next = NodePtr;
        Head = NewNode;
}

I think this should fix your problem, because, right now, your application does not take into account the condition that the m_ssan being passed to the function is the lowest value in the list.

I didn't give this a try yet, but let me know if it works.

Sincerely,
Alexander Wiseman

Est melior esse quam videri
It is better to be than to seem

Nick Parker31-Oct-02 15:19

Re: Linked List Problem (PROBLEM SOLVED -- THANKS TO ALL)

31-Oct-02 15:19

Thanks Alexander, I just tried that however it is still puking. I am not sure why as this looks like it makes sense. Confused | :confused:

Nick Parker

May your glass be ever full.
May the roof over your head be always strong.
And may you be in heaven half an hour before the devil knows you’re dead. - Irish Blessing

KarstenK1-Nov-02 1:00

KarstenK

1-Nov-02 1:00

Try to trace what you are doing! Smile | :)

If the statement "while (NodePtr != NULL && NodePtr->ssan < m_ssan)" is false ( NodePtr->ssan >= m_ssan )than PreviousNode is not set.

if m_ssan is a new maximum you only break if NotePtr->Next gets somewhere Null.

Frustrating new operator problem

Sparticus31-Oct-02 12:18

Sparticus

31-Oct-02 12:18

Hi all. I'm trying to create a simple stack template class. Yes, I can hear your remarks about just using the STL, but I have my reasons. Anyway, I'm simply trying to allocate memory to grow the stack array, but keep getting the same runtime error:

Unhandled exception at 0x0046a470 in StackTest.exe: 0xC0000005: Access violation reading location 0x00000000.

The call stack currently looks like this:

StackTest.exe!strlen() Line 78 Asm
StackTest.exe!exception::exception(const exception & that={...}) + 0x31 C++
StackTest.exe!std::bad_alloc::bad_alloc(const std::bad_alloc & __that={...}) + 0x13 C++
StackTest.exe!std::_Nomemory() Line 8 + 0xd C++
StackTest.exe!operator new(unsigned int size=240) Line 15 C++
StackTest.exe!operator new[](unsigned int count=240) Line 7 + 0x9 C++
StackTest.exe!CStack<int,30>::resize(unsigned int nNewSize=60) Line 75 + 0xc C++
StackTest.exe!CStack<int,30>::push(int & tData=8) Line 26 C++
StackTest.exe!main() Line 33 C++
StackTest.exe!mainCRTStartup() Line 259 + 0x19 C
kernel32.dll!GetCurrentDirectoryW() + 0x44

I assume from this information that there isn't enough memory available to make the allocation, but this is only the second new call that I make from the start of the program. Also, I'm only trying to allocate 240 bytes of data. Here's the code for the resize() function:

template < typename T, int INCREMENT ><br />
void CStack< T, INCREMENT >::resize( size_t nNewSize )<br />
{<BLOCKQUOTE>// Make sure the new size is valid<br />
	if ( nNewSize == m_nCapacity )<br />
		return;<br />
	else if ( nNewSize < INCREMENT )<br />
		nNewSize = INCREMENT;<br />
<br />
	T		*pNewStack;		// Pointer to the new stack<br />
	size_t		nMinSize;		// Minimum copy size<br />
<br />
	nMinSize = nNewSize < m_nCapacity ? nNewSize : m_nCapacity;<br />
<br />
	// Allocate the new stack<br />
	pNewStack = new T[ nNewSize ];<br />
	<br />
	// Move the old data into the new stack<br />
	memmove( pNewStack, m_pStack, nMinSize*sizeof(T) );<br />
<br />
	// Deallocate the old stack<br />
	delete [] m_pStack;<br />
<br />
	// Point to the new stack<br />
	m_pStack = pNewStack;</BLOCKQUOTE>}

Class Variables:
m_nCapacity = 30
m_nSize = 30
INCREMENT = 30

I appreciate any insite that anyone can provide. Thanks!

-Michael Anderson-
完成の円

Re: Frustrating new operator problem

ian mariano31-Oct-02 12:27

ian mariano

31-Oct-02 12:27

You can enable the debug CRT checks for memory leaks[^], and some of the other Memory Dumping/checking stuff from there. Maybe that will help on why you're unable to allocate using new.

"The greatest danger to humanity is humanity without an open mind."
- Ian Mariano

http://www.ian-space.com/

Re: Frustrating new operator problem

Tim Smith31-Oct-02 12:38

Tim Smith

31-Oct-02 12:38

I would doubt that you are out of memory unless you have a leak. You might be over running an allocated memory region and thus trashing the memory manager.

Tim Smith

I'm going to patent thought. I have yet to see any prior art.

dialogs

Lucky200231-Oct-02 10:12

31-Oct-02 10:12

hello,

is there a simple way, how different dialogues can be linked in a program?

lucky

Christian Graus31-Oct-02 10:25

31-Oct-02 10:25

Linked how ? Talk to one another ? I presume they are modeless ? They can just hold pointers to each other, provided by the host window. If that's not what you want, explain further what you're trying to do, so we can help.

Christian

No offense, but I don't really want to encourage the creation of another VB developer. - Larry Antram 22 Oct 2002

Hey, at least Logo had, at it's inception, a mechanical turtle. VB has always lacked even that... - Shog9 04-09-2002

During last 10 years, with invention of VB and similar programming environments, every ill-educated moron became able to develop software. - Alex E. - 12-Sept-2002

Lucky200231-Oct-02 10:33

31-Oct-02 10:33

They can just hold pointers to each other

this i still have, when the first dialog is linked with the second dialog, everything is fine, but when the first is linked with the second and third dialog, the program is terminated.

what´s wrong?

lucky

Christian Graus31-Oct-02 10:50

31-Oct-02 10:50

Why do you have three dialogs up ?

Lucky2002 wrote:
what´s wrong?

1. It's probable that a pointer you're passing around is becoming invalid for some reason.
2. You haven't posted any code, which makes it hard to do more than guess.

Christian

No offense, but I don't really want to encourage the creation of another VB developer. - Larry Antram 22 Oct 2002

Hey, at least Logo had, at it's inception, a mechanical turtle. VB has always lacked even that... - Shog9 04-09-2002

During last 10 years, with invention of VB and similar programming environments, every ill-educated moron became able to develop software. - Alex E. - 12-Sept-2002

Lucky200231-Oct-02 11:03

31-Oct-02 11:03

I believe that the first point is my problem.I think, I must give a value to the pointers (if they be produced). But how? (I´m sorry, but I have the code not here)

lucky

Christian Graus31-Oct-02 11:10

31-Oct-02 11:10

Unused pointers should always be set to NULL, and checked for NULL before use. Also, ::IsWindow will tell you if a pointer is a valid window ( which a dialog is ). Finally, show and hide your modeless dialogs so the pointer does not change, rather than destroying and recreating them.

Christian

No offense, but I don't really want to encourage the creation of another VB developer. - Larry Antram 22 Oct 2002

Hey, at least Logo had, at it's inception, a mechanical turtle. VB has always lacked even that... - Shog9 04-09-2002

During last 10 years, with invention of VB and similar programming environments, every ill-educated moron became able to develop software. - Alex E. - 12-Sept-2002

Lucky200231-Oct-02 11:25

31-Oct-02 11:25

i am confused. Unsure | :~

can you give me an example of it

(They can just hold pointers to each other, provided by the host window),

where also the pointers are adjusted to zero?

thank you very much
lucky

Christian Graus31-Oct-02 11:33

31-Oct-02 11:33

Lucky2002 wrote:
where also the pointers are adjusted to zero?

In the constructor.

MyDialog1::MyDialog1()
{
pDialog2 = NULL;
}

Then presumably the main window when it creates dialog2, also passes the pointer to dialog1. In dialog1, you do this

{
if (pDialog2 && ::IsWindow(pDialog2))
pDialog2->SomeMethod(nSomeInt);
}

Finally, when the main program wants to get rid of a window, it calls ShowWindow(SW_HIDE); and when it wants to show it does this

if (m_pDialog1)
m_pDialog1->ShowWindow(SW_SHOW);
else
{
// Create the dialog
}

Christian

No offense, but I don't really want to encourage the creation of another VB developer. - Larry Antram 22 Oct 2002

Hey, at least Logo had, at it's inception, a mechanical turtle. VB has always lacked even that... - Shog9 04-09-2002

During last 10 years, with invention of VB and similar programming environments, every ill-educated moron became able to develop software. - Alex E. - 12-Sept-2002

Lucky20021-Nov-02 8:07