Nested Linked list type pointers initialization problem

[Nelvin]

I am having problem with initializing the linked list (*exam and *subject) through the constructor of Student class, i tried by creating two new linked lists (sub and exm) and assign their addresses to both pointers (subject and exam)(refer to student class constructor), however i had a problem where the both linked lists contains garbage values such as count in exam linked list = -853218796854 instead of getting 0 the codes is given below... Each classes in different header file.

Student class:

  class Student {		
public:

        char name[30];	
        char id[10];
	char course[3];
	char phone_no[10];
	double current_cgpa; 
	int currentCreditHours;  
	int totalCreditsEarned; 
	DLL<Exam>	*exam;
	DLL<Subject> *subject;

	Student();
	
};

Student::Student(){
	
	//To set name to empty
	for(int count = 0; count < 30; count++){
		name[count] = ' ';
	}
	//To set course to empty
	for(int count2 = 0; count2 < 3; count2++){
		course[count2] = ' ';
	}
	//To set phone number to empty
	for(int count3 = 0; count3 < 10; count3++){
		phone_no[count3] = ' ';
	}

	id[0] = 0;
	id[1] = '\0';
	current_cgpa = 0;
	totalCreditsEarned = 0;
	currentCreditHours = 0;

	DLL<Subject> sub;
	DLL<Exam> exm;
	subject = &sub;
	exam = &exm;
	
}

Subject class:

class Subject{

public:
	char subject_code[8];
	char subject_name[256];
	int credit_hours;
	double marks;
	double attendance;
	double fees;
	bool payment;
	Subject();
	
	
};

Subject::Subject(){
	
	//To set subject code to empty
	for(int count = 0; count < 8; count++){
		subject_code[count] = ' ';
	}
	//To set subject name to empty
	for(int count2 = 0; count2 < 256; count2++){
		subject_name[count2] = ' ';
	}

	credit_hours = 0;
	marks = 0;
	attendance = 0;
	fees = 0;
	payment = false;
}

Exam class

class Exam {		
public:

	int trimester; //1 = jan, 5 = may and 10 = oct
	int year;
	int totalcredit;
	double gpa;
	int numOfSubjects; //for one trimester
	Subject sub[6]; //list of subjects taken by student in a semester
	Exam();
	

};

Exam::Exam(){
	trimester = 0;
	year = 0;
	gpa = 0.0;
	numOfSubjects = 0;
	totalcredit = 0;
}

DLLNode class:

template <class T>
class DLLNode {
	public:
		T		item;
		DLLNode<T>	*next;
		DLLNode<T> *prev;
		DLLNode(T);
};

template <class T>
DLLNode<T>::DLLNode(T newItem) {
	item = newItem;
	next = NULL;
	prev = NULL;
}

DLL class

template <class T>
class DLL {
	private:
		int		count;
		DLLNode<T>	*head;
		DLLNode<T>	*find(int);
	public:
		DLL();
		~DLL();
		
};

template <class T>
DLL<T>::DLL() {
	head = NULL;
	count = 0;
}

template <class T>
DLL<T>::~DLL() {

	for(int i=1; i<=size(); i++)
		remove(1);

	head = NULL;
}

[discofire]

You are assigning your exam and subject pointers to local variables whose scope expires at the end of the constructor. You need to use new to create a new instance for subject and exam.

Put the following into your constructor:

subject = new DLL<Subject>;
exam = new DLL<Exam>;

And remove the sub and exm vars you are using now.

[Nelvin]

oh nice now it works , thanks, been working this thing for straight 12 hours tried your method before it has some syntax error ,was wondering why and stop using that, guess i type something wrong LOL , thanks again man!

[Nelvin]

after it works, i take a rest, after that now i check again i had another problem, for all students with exam linked list are point to same memory address, so when i set new updated student with added exam records for a particular student, all other students also get the exam records, i apologize for my English, maybe its hard to understand.

DLL<Student> aStudent;

inside first node of aStudent:
exam with memory address 0x00385130

inside second node of aStudent:
exam with memory address 0x00385130

..... all exam nodes in aStudent will have the same record , so what should i do to avoid that?

[cire]

..... all exam nodes in aStudent will have the same record , so what should i do to avoid that?

Chances are something is off in the code that is responsible for inserting data into the list.

[Nelvin]

Any example?

[cire]

Any example?

You want me to give you an example using the code you haven't supplied? My crystal ball is out for repairs.

[Nelvin]

I actually tried, Student class contains 2 more sub linked list , which are exam and subject, for this piece of code i only add exam into student, and all other student can access to a particular student exam in linked list , hope you can understand.

bool InsertResult(char *filename, DLL<Student> *dlist){
	ifstream filetxt;
	Student tmp;
	Exam atmp;
	filetxt.open(filename);
	if(!filetxt){
		cout<<"Can not open the file"<<endl;
		return false;
	}

	while(!filetxt.eof()){
		
		Student aStudent,tmpstudent;
		Exam aExam;
		double cgpa;
		//char id[10];

		filetxt>>tmpstudent.id;
		for(int i =1;i<=dlist->size();i++){
			dlist->get(i,aStudent);
			if(strcmp(aStudent.id,tmpstudent.id)==0){
				
				filetxt>>aExam.trimester;
				filetxt>>aExam.year;
				filetxt>>aExam.numOfSubjects;

				for(int x = 0;x<aExam.numOfSubjects;x++){
					filetxt>>aExam.sub[x].subject_code;
					filetxt>>aExam.sub[x].subject_name;
					filetxt>>aExam.sub[x].credit_hours;
					filetxt>>aExam.sub[x].marks;
				}
				
				aExam.calculateGPA();
				aStudent.exam->insert(aExam);
				dlist->set(i,aStudent);
			
			}

			
		}
		
	}
	
	return true;
}