Thread: Linked List Reference Pointer problems

Hi All

I am loading a linked list from file pushing to the list from a reference pointer

However when i load the file for 2nd time (for debugging purpose to see if it rejects duplicates) one of my data got corrupted

The first time i load the file it loads perfectly fine

The 2nd time i load the employee code became -842150451, and the entire validation failed can anyone guide me on how to solve this problem?

Code:

int loadEntryForText(char *str , struct EmployeeData ** emp)
{
	int n, exist, code;
	int count = 0;
	char field[30];
	
	struct EmployeeData* currentEmp = *emp;
	

	struct EmployeeData* newEmp = NULL;
	struct Pay* newData = NULL;
	struct Date* dob = NULL;

	newEmp = malloc(sizeof(struct EmployeeData));
	newData = malloc(sizeof(struct Pay));
	dob = malloc(sizeof(struct Date));

	//Start string parsing
	while (sscanf(str, "%29[^|]%n", field, &n) == 1 ){
		//printf("field = \"%s\"\n", field);

		switch (count){
			case 0:
				code = atoi(field);
				
				for (currentEmp=*emp; currentEmp!=NULL; currentEmp=currentEmp->nextElement){ 
					if (code == currentEmp->code){ //Check if employee code exists
						printf("\n\tThe employee code: %d you have entered already exist, \n\tand thus this entry will not be added.\n\n\t", code);
						exist = TRUE;
						pause();			
					}
					else{
						exist = FALSE;
						newEmp->code = code;
					}	
				}
				//printf("%d\n", newEmp->code);
				break;
			case 1:
				newEmp->name = (char*)malloc((strlen(field)+1)*sizeof(char));
				strcpy(newEmp->name, field);
				//printf("%s\n", newEmp->name);
				break;

			case 2:
				newEmp->age = atoi(field);
				//printf("%d\n", newEmp->age);
				break;
			
			case 3:
				dob->day = atoi(field);
				//printf("%d\n", dob->day);
				break;
			
			case 4:
				dob->month = atoi(field);
				//printf("%d\n", dob->month);
				break;

			case 5:
				dob->year = atoi(field);
				//printf("%d\n", dob->year);
				break;
			
			case 6:
				newEmp->jobCat = field[0];
				//printf("%c\n", newEmp->jobCat);
				break;

			case 7:
				newEmp->basicPay = atof(field);
				//printf("%lf\n", newEmp->basicPay);
				break;
			
			case 8:
				newEmp->hours = atoi(field);
				//printf("%d\n", newEmp->hours);
				break;

			case 9:
				newData->otHours = atoi(field);
				//printf("%d\n", newData->otHours);
				break;

			case 10:
				newData->otPay = atof(field);
				//printf("%lf\n", newData->otPay);
				break;

			case 11:
				newData->weeklyPay = atof(field);
				//printf("%lf\n", newData->weeklyPay);
				break;
				
		}
		count++;
		str += n; /* advance the pointer by the number of characters read */
		if ( *str != '|' )
		{
			newEmp->dataElement = newData;
			newEmp->dob = dob;
			newEmp->nextElement = *emp;
			*emp = newEmp;
			
			break; // didn't find an expected delimiter
		}
		++str; /* skip the delimiter */
	}

	return 1;
}

Hi, i understand that there is a memory leak in my application but i cannot find out where is the leak... can anyone help me??

You're not giving enough information to tell you exactly where your mistake is but fact is:

Code:

for (currentEmp=*emp; currentEmp!=NULL; currentEmp=currentEmp->nextElement){

Here you check for currentEmp!=NULL that means that you expect an element where nextElement is set to NULL.
I can't see anywhere that you set nextElement to NULL.
On the other hand

Code:

			newEmp->nextElement = *emp;

Makes me think that this is supposed to be a circular linked list.
Kurt

This are my structures

Code:

struct EmployeeData
{	
	int		code;		/* Employee Code */
	char *	name;		/* Employee Name */
	int		age;		/* Employee Age	 */ 
	double	basicPay;	/* Basic pay of Employee */
	char	jobCat;		/* Job Category in char of Employee */
	int		hours;		/* Hour works by Employee */

	struct	Date *			dob;			/* Date of birth data element */
	struct	Pay *			dataElement;	/* Employee Pay data element */
	struct	EmployeeData *	nextElement;	/* Linked List, next element */
};

/*
Structure for Pay data
*/
struct Pay{

	int		otHours;	/* Overtime hours */
	double	weeklyPay;	/* Weekly pay */
	double	otPay;		/* Overtime pay */
};

/*
Structure for Date
*/
struct Date{
	int  month;	/* Month of year */
	int  day;	/* Day of month */
	int  year;	/* year */
};

This is what my lecturer taught me to do.. to push using a reference pointer

Code:

	//PUSH
	newEmp->nextElement = *user;
	*user = newEmp;

I have another problem that is whenever i try to delete an element

Code:

void removeElement(int n, struct EmployeeData* list)
{
	struct EmployeeData *previous = list;
	
	while(previous != NULL)
	{
		if(previous->code == n)
		{
			free(previous);
			printf("\n\n\tEmployee %d successfully deleted\n\t", n);
			break;
			return;
		}
		else
		{
			previous = previous->nextElement;
		}
	}

	if(previous == NULL )
	{
		printf("\n\tThe employee code you have entered does not exist.\n\n\t");

	}
}

After i delete the element when i display a counter

Code:

int listLength(struct EmployeeData* head) {

	struct EmployeeData* current = head;
	int count = 0;

	while (current != NULL) {
		count += 1;
		current = current->nextElement; //Error Reading an element, I have already freed the pointer but i get a error reading exception here
	}

	return count;
}

Hi, how do u deal with those.. i tried alot of things but it just give me the same exception

Hi, i could delete now but not the 1st element as pointed out by u guys can anyone tell me guide me??

Code:

void removeElement(int n, struct EmployeeData ** list)
{
	struct EmployeeData *previous = *list;
	struct EmployeeData *current = previous->nextElement;
	
	while(previous != NULL)
	{
		if (previous->code == n)
		{
			
			free(previous); //I am confused, the 1st element wouldnt delete for previous 
			printf("\n\n\tEmployee %d successfully deleted\n\t", n);
			break;	
		}

		else if(current->code == n)
		{
			previous->nextElement = current->nextElement;
			free(current);
			printf("\n\n\tEmployee %d successfully deleted\n\t", n);
			break;		
		}
		else
		{
			previous = current;
			current = current->nextElement;
		}
	}

	if(current == NULL )
	{
		printf("\n\tThe employee code you have entered does not exist.\n\n\t");

	}
}

Hi, i tried alot of things based on ur pseudo and its not working.. can you point me to a tutorial or something with some sample codes? its getting frustating