[j7x]

I was using MS Visual C++ 6.0 for the first time for simulating queue using a singly linked list. The code runs fine in Turbo C++ IDE 3.0. But it's showing me the following message whenever I try to delete an element.



Here's my code.

#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
#include<process.h>
#define MAX 10

struct linkedqueue
{
	int data;
	struct linkedqueue *next;
};

typedef struct linkedqueue *q;
int stat=0;

q insq(q hNode)
{
	q temp,cur;
	temp=(q)malloc(sizeof(q));

	if(stat==MAX)
	{
		printf("\nQueue_Overflow_Error. Re-run the program.\n");
		getch();
		return hNode;
	}
	stat++;
	cur=hNode;

	printf("\nEnter the value:\n");
	scanf("%d",&temp->data);
	temp->next=NULL;

	if(hNode==NULL)
	{
		return temp;
	}

	if(stat==1)
	{
		cur->next=temp;
		return hNode;
	}

	while(cur->next!=NULL)
		cur=cur->next;

	cur->next=temp;
	return hNode;
}

q delq(q hNode)
{
	q cur;
	
	if(stat==0)
	{
		printf("\nQueue_Underflow_Error.\n");
		return hNode;
	}

	if(stat==1)
	{
		printf("\nDeleted %d.\n",hNode->data);
		free(hNode);
		return NULL;
	}

	printf("\nDeleted %d.\n",hNode->data);
	cur=hNode;
	hNode=hNode->next;
	free(cur);
	return hNode;
}


void dispq(q hNode)
{
	q cur;

	if(stat==0)
	{
		printf("\nQueue_Empty_Error.\n");
		return;
	}
	cur=hNode;
	printf("\nThe queue elements are:\n");

	while(cur!=NULL)
	{

		printf("\n\t%d",cur->data);
		cur=cur->next;
	}
}
		

void main()
{

	q fNode;
	int opt;
	fNode=NULL;

	system("cls");
	while(1)
	{
		system("cls");
		printf("\nQueue counter: %d.\n\n",stat);
		printf("\nMenu:\n");
		printf("\n\t1. Insert\n\t2. Delete\n\t3. Display\n\t0. Exit\n\n");
		printf("\nInput please: ");
		scanf("%d",&opt);

		switch(opt)
		{
			case 1:		fNode=insq(fNode);
						break;
			case 2:		fNode=delq(fNode);
						getch();
						break;
			case 3:		dispq(fNode);
						getch();
						break;
			case 0:		exit(100);

			default:	printf("\nInvalid Input.\n");
						getch();
						break;
		}
	}
}
		

What could be the possible error?

[hackterr]

I think what this error is trying to say is that you have over written a block of allocated memory.
Could be because of a size mismatch in data and deletion
or could be an error due to some missing declaration
If any of the members is moved outside of the class, the message might disappear.
Is it occurring for a particular data or all data?

This post has been edited by hackterr: 03 November 2009 - 12:53 PM

[JackOfAllTrades]

Bet all of this will boil down to this:

typedef struct linkedqueue *q;

confusing the issue, because this:

temp=(q)malloc(sizeof(q));

is not allocating the amount of memory you think.