Linked List Problem

[josh26757]

I am building a program for my brother to edit a few things on his website that I do not want to be bothered with. The one I am working on now is the EVENTS page. What is going on is that I am reading a JavaScript file and as the lines are called the elements are broken down and stored into a linked list. Once the editing is done the file is cleared and rewritten. A default page is saved as a backup if any problems arise. The problem I am having has to be me being stupid. I am in a function making a new node for the linked list. I ask the user for all the inputs the try to assign the next and last attributes to the node. At that point the program crashes? I have no idea why.

void NewEvent(Event *list)
{
    Event *NewEvent = new Event;
    NewEvent = SetEvent();/// gets the user data for the event
    NewEvent->next = list;
    list->last = NewEvent; /// this is where the debugger catches a problem
    list = NewEvent;
    WriteEventFile(list);

}

I will post all the code if the problem is not an obvious one.

[Paul McKenzie]

You could have saved yourself all of this trouble and just use std::list.

#include <list>

http://www.cplusplus.com/reference/stl/list/

Regards,

Paul McKenzie

[josh26757]

You could have saved yourself all of this trouble and just use std::list.

#include <list>

http://www.cplusplus.com/reference/stl/list/

Regards,

Paul McKenzie

this is very true! But being a beginner I am trying to fully understand the basics and learn from problems like this. Any suggestions or is more code needed? I feel like I am missing some rule here.

[josh26757]

Here is the function called "IN" the current function:

Event *SetEvent()
{
    string event = "", location = "", date = "", time = "", note = "";
    Event *New = new Event;

    cout<<"Please Enter The Event Name\n";
    while(event == "")
     getline(cin, event);

    cout<<"Please Enter The Event Location\n";
    while(location == "")
     getline(cin, location);

    cout<<"Please Enter The Event Date\n";
    while(date == "")
     getline(cin, date);

    cout<<"Please Enter The Event Time\n";
    while(time == "")
     getline(cin, time);

    cout<<"Please Enter Any Additional Notes You Want Added\n";
    while(note == "")
     getline(cin, note);

    New->date = "Date:" + date;
    New->event = "Event:" + event;
    New->location = "Location:" + location;
    New->note = "Note:" + note;
    New->time = "Time: " + time;
    New->next = NULL;
    New->last = NULL;
    return New;
}

Before this function was a simple menu and if...else statement.
This is the last function call to write the file, but again the problem lies before this.
The write function rely on a one event per line format.

Event *WriteEventFile(Event *list)
{
    fstream myfile(EventJava, ios::out);
    ///formate beginning////////////////////////////////////////////////
    myfile<<"function events(){"<<endl
          <<"document.getElementById('center').innerHTML = '<p>'"<<endl;
   ///END FORMAT///////////////////////////////////////////////////////
   ///WRITING BODY/////////////////////////////////////////////////////
    while(list != NULL)
    {
        myfile<<"+"<<"'"<<list->event<<"<br>"<<list->location<<"<br>"<<list->date
          <<"<br>"<<list->time<<"<br>"<<list->note<<"<br><br>"<<"'"<<endl;
        list = list->next;
    }
    ///END OF BODY/////////////////////////////////////////////////////
    ///ENDING FORMAT///////////////
    myfile<<"+'</p>';}"<<endl;
    myfile.close();
    ///END ////////////////////////
}

The struct used for the Linked List -->

struct Event{
     string event, date, location, time, note;
     Event *next;
     Event *last;
};

[Paul McKenzie]

this is very true! But being a beginner I am trying to fully understand the basics and learn from problems like this. Any suggestions or is more code needed? I feel like I am missing some rule here.

Let me ask you:

Is your goal

1) To finish your program for your brother's website, bug-free and easy to maintain, probably in a matter of hours, if not minutes,

or

2) learn C++ up to the intermediate level, which may take weeks if not months, so that you know how to handle dynamically allocated memory properly?

Professional C++ programmers use std::list, and that is part of the "basics". Those basics entail learning how to use the C++ standard library properly.

Dynamic memory allocation and properly using pointers is not a beginner topic. Leave that alone until you take a data structures course in school. In the C++ programming world, most programmers use the standard library.

Regards,

Paul McKenzie

[josh26757]

Bug free is obviously the goal. I don't think I am that far from the program working though. It seems like the solution would be easy for a experienced programmer. If you feel the solution would be harder than re-writing with the template then I am open to do so.

[josh26757]

Dynamic memory allocation and properly using pointers is not a beginner topic. Leave that alone until you take a data structures course in school. In the C++ programming world, most programmers use the standard library.

Regards,

Paul McKenzie

I guess I should be patient because my next semester is algorithms and data structures.

[Paul McKenzie]

The struct used for the Linked List -->

struct Event{
     string event, date, location, time, note;
     Event *next;
     Event *last;
};

Here is an example of what I'm referring to:

#include <list>
#include <string>

struct Event
{
     std::string event, date, location, time, note;
     Event(const std::string& event_,
               const std::string& date_,
               const std::string& location_,
               const std::string& time_,
               const std::string& note_) :
             event(event_), date(date_), location(location_),
             time(time_), note(note_) { }
};

typedef std::list<Event> EventList;

int main()
{
   EventList evList;

   // add 3 events to the eventList linked list
   evList.push_back(Event("Event1", "","","",""));
   evList.push_back(Event("Event2", "","","",""));
   evList.push_back(Event("Event2", "","","",""));
}

I just added 3 Events to a linked list. I know this works correctly without even compiling or running it. Why? Because it is guaranteed to work due to usage of standard library, and not my home-made linked list which could have bugs.

No memory leaks, no pointers, no calls to new[]/delete[], nothing. You can also remove items from the linked list, sort it, etc.

Regards,

Paul McKenzie

[josh26757]

Thanks, I had already visited the reference and understand why even a professional would choose to use this. Type errors just happen and create bugs so this tested template makes since. Thanks for the great example. I am already rewriting the code and will let you know what I come up with for further criticism. Thanks again!