OK, I'm trying to write a program and I'm stuck. When I try to output, I get a segmentation fault. The program is supposed to use pointers and linked lists. I have 2 files that I need to read in (the data is some names and ages), then I need to compare the 2 lists and output the differences. Since the data is heterogenous, I need to create structs to fill the array or whatever. I'm VERY confused so any help would be fantastic. Feel free to change/manipulate any of the code. THANK YOU... here is the source (incomplete):

#include <iostream>
#include <fstream>
#include <string>
using namespace std;


struct listnode;
typedef listnode * nodeptr;
struct listnode
{
string name;
int age;
nodeptr next;
};

ifstream fin1;
ifstream fin2;
const int size = 0;
void fillstruct1(ifstream& fin1, nodeptr& temp1);
void fillstruct2(ifstream& fin2, nodeptr& temp2);
void add2end(nodeptr& head, nodeptr newptr);
int main()
{

nodeptr headptr1 = NULL;
nodeptr headptr2 = NULL;
nodeptr temp1 = NULL;
nodeptr temp2 = NULL;
nodeptr last1 = NULL;
nodeptr last2 = NULL;

fin1.open("myfile1prog2.dat");
if(!fin1.fail())
{
cout << "Reading file one...complete." << endl;
}
fin2.open("myfile2prog2.dat");
if(!fin2.fail())
{
cout << "Reading file two...complete." << endl;
}


fillstruct1(fin1, temp1);
add2end(headptr1, temp1);
while(!fin1.eof())
{
fillstruct1(fin1, temp1);
add2end(headptr1, temp1);
}
cout << "Structure one filled successfully!" << endl;

fillstruct2(fin2, temp2);
add2end(headptr2, temp2);
while(!fin2.eof())
{
fillstruct2(fin2, temp2);
add2end(headptr2, temp2);
}
cout << "Structure two filled successfully!" << endl;
}

// Functions to fill structures

void fillstruct1(ifstream& fin1, nodeptr& temp1)
{
if(!fin1.eof())
{
temp1 = new listnode;
fin1 >> temp1->name;
fin1 >> temp1->age;
temp1 = temp1->next = NULL;
}
}

void fillstruct2(ifstream& fin2, nodeptr& temp2)
{
if(!fin2.eof())
{
temp2 = new listnode;
fin2 >> temp2->name;
fin2 >> temp2->age;
temp2 = temp2->next = NULL;
}
}

// Function to link nodes

void add2end(nodeptr& head, nodeptr newptr)
{
nodeptr temp;
if(head == NULL)
{
head = newptr;
}
else
{
temp = head;
while(temp->next != NULL)
{
temp = temp->next;
}
temp->next = newptr;
}
return;
}

Here are the two files. Myfile1prog2.dat & Myfile2prog2.dat

myfile1prog2.dat:
Bill 29
Damion 666
Sue 27
Beth 11
Sue 41
Mike 55
Al 20
Julie 39
Tom 67
Peter 80
Ellen 53
Alicia 7
Megan 8
Bridget 44

myfile2prog2.dat:
Bill 29
Damion 666
Sue 27
Beth 11
Sue 41
Mike 55
Alex 20
Julie 39
Tom 67
Peter 80
Ellen 56
Alicia 7
Megan 8

Seg faults are ususally memory accesses that are outside of allocated memory. (says the resident g33k). For exaplme accessing element 101 of an array that are only 100 elements big. just wait for the program to try and acess a bit of memory thats allready owned by something else and thats ur seg fault.

Does this help?

Edit: null pointers are classics for this

pimp, im really an amateur c++ programmer and that helped explain the problem, but i dont know how to fix it

Hey mate,

If you are doin this for fun it strikes me that u might not want a full answer, do you just want a nudge in the right direction?

i would definitely like some kind of correct algorithm. if you could work the entire thing... FANTASTIC. i would be able to look at it and learn. god help me

The g33k wants to know how far it gets?

it compiles but anytime i try to output ANYTHING, i get a seg fault.

is that right?

does "Reading file one...complete." never print when you run your program?

that prints fine... i mean.. when i add more code to output headptr1 or temp1, i get a seg fault

hey space.

i can change the if to a while loop... that should take care of that. or ill just add the else... but i dont think that is giving me a seg fault... ill try tho.

I still havent written the code for OUTPUT yet... thats what i needed help on. from what i can tell, the structs are being filled... but yet... SOMETHING IS WRONG.

temp1 = temp1->next = NULL;

You sure this bit (and its friend) are right?

hey blud.. i dunno whats causing the problem but i find the best way to find these things is to use a debugger to step through the code and then you can see where the error strikes and then you can work out why its happening.

make

temp1 = temp1->next = NULL;

into

temp1->next = NULL;


that sort it?

and the temp2=blarbalr as well

teehee, my g33k says u r a very messy worker

soz mate i gotta go play games b4 sleep. Ill get the geek to have another soberer look tomorrow if that dont sort it.

!!! MADE PROGRESS.... made those changes...
then after fillstruct1 call, i stuck a "cout << temp1->name;"
in there and it outputted "Damien"


now what?

those are bool statements and i dont know how to use those

could u explain that?

Skinny d have you considered processing the data some other way?

I'm not sure why you are using C++ to do it if you dont understand it

Or is it homework

Ask your teacher then!

he wont help

What!!!?!?!?!??!?!!! Go to his supervisor and tell him your teacher isnt giving you help, your teacher will shitabrick


Unless he has some good reason not to tell u???

doesnt matter when the teacher has 10+ years.

You're going to fail......

your indentation is non existent and you haven't commented your code

sorry, that was FA help whatsoever...

But I do teach programming..not C++ though

I'll find a motorway......

well, maybe if you knew some of the professors around here you would understand. really often sad excuses for human beings. not even the book was any help. the ONLY ppl who got the assignment done were the kids who were retaking the class again. i was just asking for a little help