New Programmer, new Error

Hey guys I'm new to C and relatively new to programming, but I'm getting an error I've never seen before. All my research on this board and online has to do with something called SDL but I dont know what that is, therefore I dont use it....ha.

Anyways my code is below, its a simple linked list(Which i probably botched) and it reads from a file, adds information, and writes to the file again. I havent done the writing part yet, should be cake though.

Yikes I forgot to post the error. lol.
ERROR:
1>Linking...
1>LINK : fatal error LNK1561: entry point must be defined

Also im looking at the fputs function to write, and im thinking that it isnt right because p is a FILE pointer but its set to read. I think I need to initialize and use q for that.

Also does fputs() let me use "" to add \t for formatted file writing?

Example:
John Williams 99.80 Average.



Code is below:

Code:

---

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
struct Student{
        float ave;
        char name[128];
        struct Student* next;
}*head = (Student *)malloc(sizeof(Student));

int main()
{
struct Student* curr =(Student *)malloc(sizeof(Student));
float i = 0.0;
int count = 0, x, k;
FILE* p = fopen("studentListInFile.txt","r");
FILE* q = fopen("studentListInFile2.txt", "w");
if (curr == 0){
        printf("out of memory\n"); return -1;}
head->next = NULL;
curr=head;
curr->next = NULL;
while(!feof(p))
{               
                fgets(curr->name, 40, p);
                curr->ave = 0.0;
                curr->next = (Student *)malloc(sizeof(Student));
                curr = curr->next;
                curr->next=NULL;
                count++;

       
}
curr = head;
for (x = 0; x<count; x++)
{                printf("Enter the final average for the student: ");
                scanf("&#37;f", i);
                curr->ave = i;
                curr = curr->next;
}
curr = head;
for(k = 0; k< count; k++)
{
        fputs(curr->name, q);
        fprintf(q, "\t%f\0", curr->ave);
        curr = curr->next;
}
curr=head;
for(x=0;x<count;x++)
{
        free(curr);
        curr = curr->next;
}
free(head);
fclose(p);
fclose(q);
return 0;
}

---

Code:

---

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
struct Student{
        double ave;
        char name[128];
        struct Student* next;
}*head = NULL;

int main()
{
        struct Student* curr = (struct Student*)malloc(sizeof(struct Student));
        float i = 0.0f;
        char c;
        int count = 0, x, k;
        FILE* p = fopen("studentListInFile.txt","r");
        FILE* q = NULL;

        if (curr == 0){
                printf("out of memory\n");
                return -1;
        }

        head->next = NULL;
        curr=head;
        while(fgets(a->name, 40, p))
        {               
               
                curr->ave = 0.0f;
                curr = curr->next;
                count++;

       
        }
        curr = head;
        for (x = 0; x<count; x++)
        {
                printf("Enter the final average for the student: ");
                scanf("&#37;f", i);
                curr->ave =i;
                curr = curr->next;
        }
        curr = head;
        for(k = 0; k< count; k++)
        {
                fputs(curr->name, p);
                curr = curr->next;
        }
        free(curr);
        return 0;
}

---

Ok, now Im confused, is it the struct part? Shouldn't I cast the pointer returned by malloc as the type I would want?

Took out struct and Im still getting an error, so it has to be the whole casting. Im still confused though. Thanks for the help in advance

Ok I took out both struct keywords in the memory allocation and rebuilt the problem in another solution. If I stay in my current solution in VS 2008 i keep getting the same errors even though I had fixed them, can anyone help me with that too?

So:

Code:

---

$ gcc -o temp -Wall -Wextra temp.c
temp.c: In function ‘main’:
temp.c:24: error: ‘a’ undeclared (first use in this function)
temp.c:24: error: (Each undeclared identifier is reported only once
temp.c:24: error: for each function it appears in.)
temp.c:34: warning: format ‘%f’ expects type ‘float *’, but argument 2 has type ‘double’
temp.c:17: warning: unused variable ‘q’
temp.c:14: warning: unused variable ‘c’

---

That format warning is sneaky. And I don't know what a is supposed to be either. Do you mean curr? And you're going to have to malloc one time for every student,

Ive fixed a LOT of errors in the program, and now I get an error after inputting the first value from the user, it takes me to line 1287 in input.c

#else /* _UNICODE */
_FASSIGN( longone-1, (char*)pointer , pFloatStr, (char)decimal, _loc_update.GetLocaleT());

When i hit the break key in debug mode. Any suggestions?

From what I can make out the probable cause is

Code:

---

head->next = NULL;  /* head is a NULL pointer; its not been initialized nor does it point to an object of type struct Student */

---

If you were on UNIX it would abend with a SIGBUS.

Which still means you need to malloc one object for each student and hook them together in a list.

Ok I think I get what youre saying. I need to append the list. This is where I get confused. Since curr is going to go through the list, wont I need to create a specific named struct for each student in order for the linked list to stay intact?

Im deleting what was stored in curr when I reassign it, so Im defeating myself in the loop. Am I on the right track?


Also i think everytime the while loop goes through Ill be starting at the beginning of the file again with fgets? Am I wrong in that?

Can anyone let me know if I'm on the right track?

curr can't go through the list, because you don't have a list yet. You have to make a list, by building nodes and attaching, building nodes and attaching, building nodes and attaching, etc.

And of course fgets doesn't go back to the start of the file.

it would be a good idea to post your updated code so we can all be on the same page.

{EDIT} Updated code is at the top, thanks for the suggestion itCbitC.


Ok....but shouldnt the list be created as I initialize the next pointer in each struct?

for example

Code:

---

struct Node{
int data;
Node* next;
}

---

Should be enough to make a node member of a linked list I create in my main function right? All I would need to do is initialize a head variable, a temp(curr in my case) variable, and then when a new member is to be added on, i assign it to curr, head->next = curr, curr-> next = 0?

Im afraid this boils down to an ignorance of linked lists, and I couldnt find a tutorial for one in your guys' tutorials.

For some reason I keep thinking I have to name each member in the list to solve this problem, even though thatd be ludicrous as the list could be potentially HUGE.

Quote:

---

Originally Posted by ASURugger

{EDIT} Updated code is at the top, thanks for the suggestion itCbitC.


Ok....but shouldnt the list be created as I initialize the next pointer in each struct?

for example

Code:

---

struct Node{
int data;
Node* next;
}

---

Should be enough to make a node member of a linked list I create in my main function right? All I would need to do is initialize a head variable, a temp(curr in my case) variable, and then when a new member is to be added on, i assign it to curr, head->next = curr, curr-> next = 0?

Im afraid this boils down to an ignorance of linked lists, and I couldnt find a tutorial for one in your guys' tutorials.

For some reason I keep thinking I have to name each member in the list to solve this problem, even though thatd be ludicrous as the list could be potentially HUGE.

---

You must not be very good at looking.

Evidently I'm a terrible looker >.<, really sorry about that, i stopped after Data Structures.

So after reading the linked list tutorial, I think that my program does implement a linked list properly, with a few minor tweaks. It builds fine, but when i run the program in debug mode i get the error previously said.

Does that still have to do with my linked list even though every time I take in a new string I creat a new struct and allocate the memory for it?

Ok, in that initial while loop I'm wrong somewhere. I put break points at the beginning of the for loop to look at what was stored in the variables.

Something is wrong with my condition in the while loop and something is wrong with the way im going through the linked list. Im completely dumbfounded on both accounts.

The name variable in curr has 128 T looking characters and its point to ?? it says. For the double, im getting a memory location as its value, im assuming this is because curr as a whole is a pointer, therefore the variables inside act as such?

Im sorry for my ignorance on this and if theres a place where I can read this info, please, point me there, but currently youre the best source of information on the web.

Quote:

---

Originally Posted by ASURugger

Does that still have to do with my linked list even though every time I take in a new string I creat a new struct and allocate the memory for it?

---

It has everything to do with the fact that you do nothing of the sort. Watch:

Code:

---

while (fgets(tempname, 40, p) != NULL) {
    tempstudent = malloc(sizeof(*tempstudent));
    strcpy(tempstudent->name, tempname);
    tempstudent->ave = 0.0f;
    tempstudent->next = head;
    head = tempstudent;
}

---

You have to malloc a node for every student. (This code adds the new student to the front of the line; you'll have to change it if you want the student at the back, or sorted, or whatever.)

Code:

---

fgets(curr->name, 40, p);
                                curr->ave = 0.0;
                curr->next = (Student *)malloc(sizeof(Student));
                curr = curr->next;
                curr->next=NULL;
                count++;

---

That seems really similar to what youre doing, where am I wrong in this code here so that I don't do it again? My understanding of my code is that i take in a string and put it in curr.name, i initialize curr.ave as 0.0 and then i make a new Student in curr.next, i move curr to that new student i created and set its next pointer to null. Is that not what is happening here?

I looked at the code above again and I still think Im allocating memory for each string. Im sorry to ask a redundant question and not understand.

I was looking at the wrong updated code. The updated code in the very first post can't possibly compile, as there's no way you can do a malloc to initalize a global object, so I don't know what code you are actually running.

Quote:

---

Originally Posted by ASURugger

Code:

---

fgets(curr->name, 40, p);
                                curr->ave = 0.0;
                curr->next = (Student *)malloc(sizeof(Student));
                curr = curr->next;
                curr->next=NULL;
                count++;

---

That seems really similar to what youre doing, where am I wrong in this code here so that I don't do it again?

---

Though they look similar yet the two approaches are poles part as one adds nodes to the tail of the list while the other adds them to the head of the list.

I think I understand now. I was confused by the fact that if I assign head to element it means they are both pointing to the same address. I thought id be replacing a variable.

Thank you for your patience and help. Ill probably have more questions though... lol.

Code:

---

for (x = 0; x<count; x++)
{                printf("Enter the final average for the student: ");
                scanf_s("&#37;f", i);
                element->ave = i;
                element = element->next;
               
}

---

Ok there is a definite problem here as it produces an error saying cannot write to location 0x0000000.
Also count is not incrementing as I think it should, I will link my new while loop, mostly borrowed from tab.

Code:

---

while(!feof(pread))
{
        fgets(tempname, 128, pread);
        for(x = 0; x<128;x++)
        {
                if(tempname[x] == '\n')
                {
                        tempname[x] = '\0';
                        break;
                }
        }
        count++;
        strcpy(element->name, tempname);
        element->ave = i;
        element->next = head;
        head = element;
       
}

---

I added the for loop to add a null terminator to the string, i think that would work. count shows up as only 1. Should be 3 from my input file which has 3 names separated by '\n'.
Im assuming this is a pointer error in my linked list because i get the output "Enter student average" but when I input the double number the error occurs and the program stops working. Any suggestions?

Quote:

---

Originally Posted by ASURugger

Code:

---

for (x = 0; x<count; x++)
{                printf("Enter the final average for the student: ");
                scanf_s("%f", i);
                element->ave = i;
                element = element->next;
               
}

---

Ok there is a definite problem here as it produces an error saying cannot write to location 0x0000000.
Also count is not incrementing as I think it should, I will link my new while loop, mostly borrowed from tab.

Code:

---

while(!feof(pread))
{
        fgets(tempname, 128, pread);
        for(x = 0; x<128;x++)
        {
                if(tempname[x] == '\n')
                {
                        tempname[x] = '\0';
                        break;
                }
        }
        count++;
        strcpy(element->name, tempname);
        element->ave = i;
        element->next = head;
        head = element;
       
}

---

I added the for loop to add a null terminator to the string, i think that would work. count shows up as only 1. Should be 3 from my input file which has 3 names separated by '\n'.
Im assuming this is a pointer error in my linked list because i get the output "Enter student average" but when I input the double number the error occurs and the program stops working. Any suggestions?

---

Where do you allocate/assign element in the first loop?

--
Mats

But you don't malloc() any storage before copying to element->name.

Programming makes me look so stupid currently lol.

Code:

---

while(!feof(pread))
{
        fgets(tempname, 128, pread);
        element =(Student *)malloc(sizeof(Student));
        for(x = 0; x<128;x++)
        {
                if(tempname[x] == '\n')
                {
                        tempname[x] = '\0';
                        break;
                }
        }
        count++;
        strcpy(element->name, tempname);
        element->ave = i;
        element->next = head;
        head = element;
       
}

---

That looking better? I create element earlier in the main function, but im not allocating memory to it until this.

While im debugging after I execute this loop

Code:

---

for (x = 0; x<count; x++)
{                printf("Enter the final average for the student: ");
                scanf_s("&#37;f", &i);
                element->ave = i;
                element = element->next;
               
}

---

It shows i as an integer though ive defined it as a double and and its saying in the value of p <Bad Ptr>. So its a bad pointer im guessing? I dont understand whats happening under the hood too well, so I dont get these messages.

Hmmm deja vu... I remember making similar corrections to your code last time but here goes...

Code:

---

while(fgets(tempname, 128, pread))
{
        element = malloc(sizeof(Student));
        if(element)
        {
                strtok(tempname, "\n"); // include <string.h>
                count++;
                strcpy(element->name, tempname);
                element->ave = i;
                element->next = head;
                head = element;
        }
}

---