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List node error problem

Started by TheShadow Mar 22, 2003 at 10:40 AM 4 replies 250+ views

Original Post

Mar 22, 2003 at 10:40 AM

Why am i getting access violation error from windows and not debugger from the following program... what is wrong with it?

  
#include <iostream>
using std::cout;
using std::endl;

int maxnodes = 20;
int i;

struct listNode 
{    
	int data; 
	struct listNode *nextPtr;
};    

void main()
{

	listNode node[19];
	for( i = 0; i <= maxnodes; i++)
	{
		node[i].data = i;
		if(i == 19)
		{
			node[i].nextPtr = 0;
		}
		else
			node[i].nextPtr = &node[i+1];
	}

	
	listNode *iterator = &node[0];
	while (iterator != 0)
	{
		
		cout << iterator->data << endl;
	
		iterator = iterator->nextPtr;
	}  
}

I hope somebody can help me.

civguy

Mar 22, 2003 at 10:46 AM

listNode node[19];

Now node[0] is the first element, node[18] is the last element. But you''re going up to 20. That''s two more than allowed..

TheShadow

Author

TheShadow

Mar 22, 2003 at 10:48 AM

thanks again civ

CraZeE

Mar 22, 2003 at 10:52 AM

  
maxnodes = 20;   // Max set to 20!

.
.
listNode node[19];  // But u only have 19 elements!

for( i = 0; i <= maxnodes; i++) // and u check for 21 times!

{
   node[i].data = i;
   if(i == 19)   // plus u perform error check for 19 only!

   {...}
   ...
}

u may need to modify the loop to repeat i < maxnodes. may be wrong on my part, but the problem shud rvolve around that.

Mar 22, 2003 at 10:59 AM

??? What should do it???
I would do it like this:

  
struct listNode
{
    int name;
    int data;
    struct listNode *next;
};

listNode *g_firstNode;

void AddNode(int name, int data)
{
    struct listNode *node;

    if (g_firstNode == NULL)
    {
        node = g_firstNode = new listNode;
    }
    else
    {
        node = g_firstNode;
        while(true)
        {
            if (node->next == NULL)
                break;
            node = node->next;
        }
        node->next = new listNode;
        node = node->next;
    }
    node->name = name;
    node->data = data;
}

void DeleteNode(int name)
{
    struct listNode *node1;
    struct listNode *node2;

    node2=NULL;
    node1=g_firstNode;

    while(true)
    {
        if (node1->name == name)
        {
            if (node2)
                node2->next=node1->next;

            delete node1;
            break;
        }
        node2 = node1;
        node1 = node2->next;
    }
}

int GetNodeData(int name)
{
    struct listNode *node=g_firstNode;
    while(true);
    {
        if (!node)
            return 0;   // Error

        if (node->name == name)
            return node->data;
        node = node->nextNode;
    }
}

bool SetNodeData(int name, int data)
{
    struct listNode *node=g_firstNode;
    while(true);
    {
        if (!node)
            return false;   // Error

        if (node->name == name)
        {
            node->data = data;
            return true;
        }
        node = node->nextNode;
    }
}

Sorry if there are errors... I''ve just written this code and couldn''t test it...

Now, when you call these functions, there shouldn''t be any acces violation

Times change...

Excuse my poor english!

silvermace

105

silvermace

Mar 23, 2003 at 12:49 AM

here is PM 's code in C (PM stop mixing C and C++, you used 'bool', 'new', and 'delete' and you too shadow whats with the 'struct listNode' ? its depresiated in C++

)

shadow if your using C++ (im guessing -- 'using' & 'iostream')
just use STL's 'list' class, i dont see the point in re-inventing the wheel.. its part of the standard..

this code isnt tested, but it should work better than PM on a C compiler..

    
  
struct listNode
{
    int name;
    int data;
    struct listNode *next;
};

typedef struct listNode listNode_t;
typedef listNode_t* listIterator;

listIterator g_firstNode;

void AddNode(int name, int data)
{
    listIterator node;

    if (g_firstNode == NULL)
    {
        node = (g_firstNode = (listIterator) malloc(sizeof(listNode_t));
    }
    else
    {
        node = g_firstNode;
        while(1)
        {
            if (node->next == NULL)
                break;
            node = node->next;
        }
        node->next = (listIterator) malloc(sizeof(listNode_t);
        node = node->next;
    }
    node->name = name;
    node->data = data;
}

void DeleteNode(int name)
{
    listIterator node1 = NULL;
    listIterator node2 = NULL;

    node2 = NULL;
    node1 = g_firstNode;

    while(1)
    {
        if (node1->name == name)
        {
            if (node2)
                node2->next = node1->next;

            free(node1);
            break;
        }
        node2 = node1;
        node1 = node2->next;
    }
}

int GetNodeData(int name)
{
    listIterator node = g_firstNode;

    while(1)
    {
        if (!node)
            return 0;   // Error

 
        if (node->name == name)
            return node->data;
 
        node = node->nextNode;
    }
}

int SetNodeData(int name, int data)
{
    listIterator node = g_firstNode;

    while(1)
    {
        if (!node)
            return 0; // Error


        if (node->name == name)
        {
            node->data = data;
            return 1;
        }

        node = node->nextNode;
    }
}

-- a dancing person appears insane to those who cannot hear the music
http://homepages.paradise.net.nz/danu/ -- Just click it

[edited by - silvermace on March 23, 2003 1:57:00 AM]

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