C++ Access Violation Exception?

Miss k (3)
Hi all

I am getting an access violation expection error in the function code below though everything has been intilaized proporely. 

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struct queue
{
	
		long start;
		long duration;
		struct queue *next;
		struct queue *prev;
};

queue *H_queue_H;
queue *H_queue_L;
queue *H_queue_H_V;
queue *N_queue_H;
queue *N_queue_L;
queue *H_queue_head_H;
queue *H_queue_tail_H;
queue *H_queue_head_L;
queue *H_queue_tail_L;
queue *H_queue_head_H_V;
queue *H_queue_tail_H_V;
queue *N_queue_head_H;
queue *N_queue_tail_H;
queue *N_queue_head_L;
queue *N_queue_tail_L;
queue *H_queue_empty_H;
queue *H_queue_empty_L;
queue *H_queue_empty_H_V;
queue *N_queue_empty_H;
queue *N_queue_empty_L;


int Buffer_Call(int i)
{
	queue *b;
		if(i==0)
		{
			b=H_queue_empty_H;
			H_queue_empty_H=H_queue_empty_H->next; 
			b->start=currentTime;
			b->duration= currentTime +GenExpRV(mewHwait_H);
			if(H_queue_tail_H!=(queue *)NULL)
			{
				H_queue_tail_H->next=b;
				b->prev=H_queue_tail_H;
				b->next = (queue *)NULL;
				H_queue_tail_H=b;
			}
			else
			{
				H_queue_head_H=H_queue_tail_H=b;
				b->next = (queue *)NULL;
				b->prev = (queue *)NULL;
			

			}
			QH_H++;
		}
		else if(i==1)
		{
			b=H_queue_empty_L;
			H_queue_empty_L=H_queue_empty_L->next; 
			b->start=currentTime;
			b->duration= currentTime +GenExpRV(mewHwait_L);
			if(H_queue_tail_L!=(queue *)NULL)
			{
				H_queue_tail_L->next=b;
				b->prev=H_queue_tail_L;
				b->next = (queue *)NULL;
				H_queue_tail_L=b;
			}
			else
			{
				H_queue_head_L=H_queue_tail_L=b;
				b->next = (queue *)NULL;
				b->prev = (queue *)NULL;
			

			}
			QH_L++;
		}
		if(i==2)
		{
			b=H_queue_empty_H_V;
			H_queue_empty_H_V=H_queue_empty_H_V->next; 
			b->start=currentTime;
			b->duration= currentTime +GenExpRV(mewHwait_H_V);
			if(H_queue_tail_H_V!=(queue *)NULL)
			{
				H_queue_tail_H_V->next=b;
				b->prev=H_queue_tail_H_V;
				b->next = (queue *)NULL;
				H_queue_tail_H_V=b;
			}
			else
			{
				H_queue_head_H_V=H_queue_tail_H_V=b;
				b->next = (queue *)NULL;
				b->prev = (queue *)NULL;
			

			}
			QH_H_V++;
		}



		else if(i==3)
		{
			b=N_queue_empty_H;
			N_queue_empty_H=N_queue_empty_H->next;
			b->start=currentTime;
			b->duration=currentTime + GenExpRV(mewNwait_H);
			if(N_queue_tail_H!=(queue *)NULL)
			{
				N_queue_tail_H->next=b;
				b->prev=N_queue_tail_H;
				b->next = (queue *)NULL;
				N_queue_tail_H=b;

			}
			else
			{
				N_queue_head_H=N_queue_tail_H=b;
				b->next = (queue *)NULL;
				b->prev = (queue *)NULL;

			}
			QN_H++;
		}
		else if(i==4)
		{
			b=N_queue_empty_L;
			N_queue_empty_L=N_queue_empty_L->next;
			b->start=currentTime;
			b->duration=currentTime + GenExpRV(mewNwait_L);
			if(N_queue_tail_L!=(queue *)NULL)
			{
				N_queue_tail_L->next=b;
				b->prev=N_queue_tail_L;
				b->next = (queue *)NULL;
				N_queue_tail_L=b;

			}
			else
			{
				N_queue_head_L=N_queue_tail_L=b;
				b->next = (queue *)NULL;
				b->prev = (queue *)NULL;

			}
			QN_L++;
		}


		return 0;
}


The error seems to be in the following lines:

H_queue_empty_H=H_queue_empty_H->next;

H_queue_empty_L=H_queue_empty_L->next;

H_queue_empty_H_V=H_queue_empty_H_V->next;

N_queue_empty_H=N_queue_empty_H->next;

N_queue_empty_L=N_queue_empty_L->next;

but I don't understand since everything has been initialized earlier. What do you think guys? What seems to be the problem?

Any help/suggestions will be greatly appreciated :)

Thanks





hamsterman (4538)
Nothing has been initialized. Not in the code you posted anyway..
Miss k (3)
This is the initialization part for H_queue (H_queue being a double linked list). Other queues has a similar initialization process

H_queue_H= (struct queue *)malloc(max_QH_H*sizeof (struct queue));
memset(H_queue_H, 0, max_QH_H*sizeof(struct queue));
H_queue_head_H= H_queue_H;
for (i=0; i< max_QH_H-1; i++)
H_queue_H[i].next=H_queue_H+i+1;
H_queue_H[max_QH_H-i-1].next=(struct queue *) NULL;
H_queue_head_H = H_queue_tail_H=(struct queue *) NULL;
H_queue_empty_H=H_queue_H;
hamsterman (4538)
Still, this sounds like uninitialized pointer.
Try making line 25, queue *H_queue_empty_H = 0;, and adding printf("H_queue_empty_H is at %p\n", H_queue_empty_H); immediately after initialization and before line 38, to see if that pointer is initialized and if it isn't corrupted.
Last edited on
Miss k (3)
It turned out that the linked list was not intialized properly
The main error is this line:

H_queue_H[max_QH_H-i-1].next=(struct queue *) NULL;

When I exit for loop, I was setting first element's next field to NULL while I should have set the last one instead!

Thanks hamsterman :)
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