Modified LinkedList not updating in text file itself - c++

Question

The Intro:
I'm working on a Project #Student Course Registration System,
my project is based on singly linked list, with file handling.
The Problem:
I have managed to modify the nodes in LinkedList, made a separate function to update my text file. But the problem is the file is not getting updated. On the console, I do see the items updated.
I have to work around modifying the text file without making a temporary one and copying items to that, which I know how to.
P.S : I have made a function which always loads all the required Text Files into the program at startup.
Structure:
struct Student {
string stdID;
string stdName;
string stdSemester;
Student *next;
};
Main:
int main() {
Student *Head = NULL;
Student *Tail = NULL;
Course *Headd = NULL;
Course *Taill = NULL;
UpdateDirectory(Head, Tail, Headd, Taill);
Display(Head, Tail);
_getch();
string Value;
getline(cin, Value);
ModifyStudent(Value, Head);
UpdateFile(Head, Tail);
//Display(Head, Tail);
return 0;
}
Modify Function:
void ModifyStudent(string Value, Student *&Head) {
// Initialize:
Student *Curr = NULL;
Student *Temp1 = NULL;
Student *Temp2 = NULL;
Student *Obj = new Student;
if (isEmpty(Head)) {
cout << "\t\t\t\t Underflow....\n\n";
_getch();
}
else {
Curr = Head;
Temp1 = Head;
while (Curr->stdID != Value) {
Temp1 = Curr;
Curr = Curr->next;
}
if (Curr->stdID == Value) {
cout << "\t\t\t\t Student Found!!\n\n";
cout << Curr->stdID << endl; // 1324
cout << Temp1->stdID << endl; // 3424
// Modify:
cout << "\t\t\t\t Enter New Student ID : ";
getline(cin, Obj->stdID);
cout << "\t\t\t\t Enter New Student Name : ";
getline(cin, Obj->stdName);
cout << "\t\t\t\t Enter New Semester : ";
getline(cin, Obj->stdSemester);
Temp1->next = Obj;
Obj->next = Curr->next;
Curr->next = NULL;
delete(Curr);
/// Save:
cout << "\t\t\t\t Record Is Being Updated, Please Wait.......\n\n" << endl;
_getch();
}
}
}
Update File:
void UpdateFile(Student *&Head, Student *&Tail) {
Student *Temp = NULL;
fstream SFile;
SFile.open("StudentRecords.txt", ios::trunc);
if (isEmpty(Head)) {
cout << "\t\t\t\t UnderFlow\n" << endl;
}
else {
Temp = Head;
while (Temp->next != NULL) {
cout << Temp->stdID << '\t' << Temp->stdName << '\t' << Temp->stdSemester << '\n';
SFile << Temp->stdID << '\t' << Temp->stdName << '\t' << Temp->stdSemester << '\n';
Temp = Temp->next;
}
cout << Temp->stdID << '\t' << Temp->stdName << '\t' << Temp->stdSemester << '\n';
SFile << Temp->stdID << '\t' << Temp->stdName << '\t' << Temp->stdSemester << '\n';
_getch();;
}
_getch();;
}
I have even used ios::trunc, but no effect.
Thank You!

Answer 1

It is hard to say what the problem is. You did not provide the full source code; therefore we cannot compile the code.
To write a file, use the following. The file will be overwritten (this seems to be what you are looking for):
ofstream os{ "test.txt" };
if( !os )
return -1;
if( !list.write( os ) )
return -2;
Regarding your code, this is a more c++ like approach to single linked lists:
Define a data class/structure. You may want to use the data with other classes, not only with a linked list, therefore keep it separated from node:
class student_t
{
public:
string id;
string name;
string semester;
// ...
};
Define operations. One of the operations you need is write:
ostream& write( ostream& os )
{
return os
<< id << endl
<< name << endl
<< semester << endl;
}
Define a node. A node is made of data and a pointer to next node:
class node_t
{
friend class list_t; // or replace it with public:
student_t data;
node_t* pnext;
// ...
};
Add a constructor and a write method:
node_t( const student_t& s, node_t* pnext ) : data{ s }, pnext{ pnext } {}
ostream& write_data( ostream& os )
{
return data.write( os );
}
Define a list class. The only data a list class holds is the list’s head. The class will gather all list operations like write_data, push_front, display_data, etc.
class list_t
{
node_t* phead{ nullptr };
public:
void push_front( const char* id, const char* name, const char* semester )
{
phead = new node_t( student_t{ id, name, semester }, phead );
}
ostream& write( ostream& os )
{
node_t* pn = phead;
while( pn && pn->write_data( os ) )
pn = pn->pnext;
return os;
}
//...
};
And this is how you use it:
int main()
{
list_t list;
list.push_front( "J1", "Jon", "first" );
list.push_front( "S1", "Steve", "first" );
{
ofstream os{ "test.txt" };
if( !os )
return -1;
if( !list.write( os ) )
return -2;
} // the file is automatically closed here
list.push_front( "A1", "Ava", "second" );
{
ofstream os{ "test.txt" };
if( !os )
return -1;
if( !list.write( os ) )
return -2;
}
return 0;
}