Thread: FPUTS-struct node loop.

I have to make a programm that among others outputs a text stored in a struct node (line by line), in a file. I use fputs.
Here is the function PrintFile that prints the file:

Code:

void WriteFile(struct list *buffer, char *filename)             
{
        char line[MAXLINE];
        FILE *fp;
                        fp=fopen(filename,"w");
                        if (fp==NULL)
                        {
                                printf("Den einai dinaton, na ginei eggrafi sto arxeio %s!", filename);
                        }
                        else
                        {
                                int currentpos;
                                struct node *nodeM;
                                int *current;

                                fputs(line, fp);

                        }
                        fclose(fp);
}

This function just prints the last line of the text. I want to make a loop that puts each line from the first to the last, but I cant. I tried a for and a while, I put a j as the number of the line but it didn't work either. It can't be compiled or I get a segmentation fault when running.
Maybe there is something wrong with the rest of the programm! If you want some other part of the code in order to help me-I will send it, I just didn't want to add 280 lines of code for a function.
Thanks,
AA

Code:

while ( p != NULL ) {
  /* do stuff with node p */
  p = p->next;
}

This is very typical how how you traverse a linked list.

I did it but with prev instead of next as it starts from the last line, and I could not make the *next pointer while reading the file. I think it should work but : segmentation fault! I HATE SEGMENTATION FAULTS!!!
I don't know why, it doesnt work I have tryed a lot of simmilar things wich I found on codes while searching this forum but nothing works.
What do you think? Maybe I don't store the file properly???
Here is the function that reads the file:

Code:

void ReadFile(struct list *buffer, char *filename)    
{
        char line[MAXLINE];
                        struct node *nodetmp;


                FILE *fp;
                fp = fopen(filename,"r");
                if (fp==NULL)
                        printf("The file %s can't be read!", filename);
                else
                {       int size, currentpos;
                        struct node *nodeM;

//                      buffer->head=fgets(line,MAXLINE,fp);     //this is for *head! but it doesnt work!

                        while ((fgets(line, MAXLINE, fp))!=NULL)
                        {
                                nodeM=MALLOC(sizeof(struct node));

                                ++currentpos;
                                ++size;
                                nodeM->prev = buffer->tail;
//                              nodetmp = (*buffer).tail;             // this 2 lines are for next but when thy are not as a coment I get segmentation fault while reading
//                              (*nodetmp).next=nodeM;
                                buffer->tail=nodeM;

                                printf("%s",line);   //actually I don't need this line, but its to see the file while reading
                        }
                }
                fclose(fp);
}

> buffer->head=fgets(line,MAXLINE,fp); //this is for *head! but it doesnt work!
Because ALL your buffers end up pointing at the SAME LOCAL variable!
You fgets() into the local variable, then you allocate if necessary your buffer->head, then you strcpy() into it.

head is a very poor choice of name for actually storing data.

Please post your struct list next time.

These are my structs:

Code:

struct node {
        char         *line;
        struct node  *prev;
        struct node  *next;
};

struct list {
        struct node  *head;
        struct node  *tail;
        int           size;
        int     currentpos;
        char      *current;
};

head is the pointer to the first node and tail to the last. Why is it poor? Actually this is a project and it has to be made with this structs.
By the way I have starting working on this exactly one week before, and work on it whenever I have free time, but still only 2 of 7 functions are made and these do not work prperly too. I have now 3 days left and I am getting stress. So I would be glad if somebody helped me. I have read the chapter about pointers in the K&R book 3 times, but this doesn't help. I also looked at the tuts here but I cant make the functions work !

> head is the pointer to the first node and tail to the last. Why is it poor?
> buffer->head=fgets(line,MAXLINE,fp);
See the answer yet?

Try this

Code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

struct node {
  char         *line;
  struct node  *prev;
  struct node  *next;
};

struct list {
  struct node  *head;
  struct node  *tail;
  int           size;
  int     currentpos;
  char      *current;
};

struct node *makeNode ( char *line ) {
  struct node *new = malloc ( sizeof *new );
  if ( new ) {
    /* initialise a node */
    new->prev = NULL;
    new->next = NULL;
    new->line = malloc ( strlen(line) + 1 );  /* should check NULL */
    strcpy ( new->line, line );
  }
  return new;
}

void appendlist ( struct list *list, char *line ) {
  struct node *new = makeNode ( line );
  /* now add it to the list */
  if ( list->head == NULL ) {
    /* easy, list is empty */
    list->head = new;
    list->tail = new;
    list->size = 1;
  } else {
    /* fix the tail node of the list */
    list->tail->next = new;
    /* fix the previous of the new node */
    new->prev = list->tail;
    /* move the tail forward */
    list->tail = new;
    list->size++;
  }
}

void ReadFile ( struct list *list, char *filename ) {
  char buff[BUFSIZ];
  FILE *fp = fopen( filename, "r" );
  while ( fgets ( buff, BUFSIZ, fp ) != NULL ) {
    appendlist ( list, buff );
  }
  fclose ( fp );
}

void WriteFile ( struct list *list, char *filename ) {
  FILE *fp = fopen( filename, "w" );
  struct node *p = list->head;
  printf( "List as %d nodes\n", list->size );
  while ( p != NULL ) {
    fputs ( p->line, fp );
    p = p->next;
  }
  fclose ( fp );
}

int main ( ) {
  struct list mylist = { 0, 0, 0, 0, 0 }; /* empty list */
  ReadFile ( &mylist, "foo.c" );
  WriteFile ( &mylist, "bar.c" );
  return 0;
}

Salem! I don't know how to thank you.
Really thanks a lot.
It works, I have been a lot further with my project(thanks to your help I could make 2 more functions: InsertLine and DeleteLine also work perfect now, and the most important i finally understood (or I think so) how linked lists work.
I can't describe how happy I am!
Thanks again.
I owe you one!