Transferring text from file into linked list

I have to write a program for my current project that will open a file and copy the text into a linked list word by word.

The way I was thinking of doing it was by copying the text into an array and using the spaces between the words to seperate each word and store it in the list.

I was just wondering whether this is the best way of doing it as I am going to have to have a massive array to store all the text (as it is 156,000 characters).

Thanks in advance

Because file is not too long I think to read the whole file in the buffer and process buffer in a way you have described is better than to read word by word...

So I don't see a problem in the described approach

What u could do is read a single line at a time. tokensize the string and store them in the linked list. Follow the same till u reach the EOF while reading the file. Use fgets to read a line.

ssharish2005

im not exaclty sure what you mean by buffer, I was planning to read the whole text file into an array. Then when inserting it into the linked list I will split it into seperate words, this is because I need to be able to search the list to check how many times a word appears in the text.

I also need to be able to dynamically allocate the memory for the array, as my program has to be able to cope with the user inputting the name of the file.

I have written the code below to do this, but I am sure this is incorrect as the first piece seg faults at the while statement and the second piece doesn't compile as the putc 2nd statement makes a pointer from an integer without a cast.

Code:

---

char readdata(char *name){
    char *x;
    x = calloc(1, sizeof(FILE));
   
             
    FILE *ifp;
    int i = 0;
    ifp = fopen(name, "r");
   
    while ((x[i] = getc(ifp)) != EOF){
          i++;
          }
   
    return *x;
}

---

Code:

---

char readdata(char *name){
    char *x;
    x = calloc(1, sizeof(FILE));
                   
    FILE *ifp;
    int i = 0;
    char c;
    ifp = fopen(name, "r");
   
    while ((c = getc(ifp)) != EOF){
          putc(c, x[i]);
          i++;
         
          }
   
    return *x;
}

---

sizeof FILE returns number of bytes in the structure FILE, it has nothing to do with the file length
use

Code:

---

fseek(fptr, 0, SEEK_END);
size = ftell(fptr);

---

pair to determine the actual length of the open file.

Before using file pointer - check if it is not null
read the entire content of the file with fread (don't forget to check the return value)
before using allocated memory - check that the pointer returned by calloc is not null
don't forget to allocate one additional byte to put the 0 character at the end if you're going to work with the array as a string

thanks a lot for your help, I did doubt whether the calloc statement was correct. I'll give that a go and see what I come up with.

Thanks again for pointing me in hte right direction

Also don't forget to free your *alloc()ed memory when you're done with it.

cppreference.com :: malloc()
FAQ > Explanations of... > Casting malloc
FAQ > What's the difference between... > malloc and calloc?

[Code]
ifp = fopen(name, "r");
[\code]

is this line in the program before correct?

I seem to be getting a segmentation fault as a result of this line not working correctly, it is supposed to open the file that's name is stored in the char field name which has been passed into this function.

I have the text file in the same folder as program is running from although this is in my documents and not at the root, does this make any difference.

Thanks again

edit: thanks for the headsup dwks, I was leaving it till the end until I knew the exact program structure so I know when to free the memory but I will comment in a reminder now so I don't forget

If the file couldn't be opened, fopen returns NULL. Since you don't check for that, it could quite conceivably cause a segmentation fault.

Is it possible to pass pointers between functions?

the readdata function has been fixed so it works properly now but I can't seem to get it to pass a pointer back to the main function, I have included the code in my main function below.

Thanks

Code:

---

int main(){
    char a[30];
    char *y;
    scanf("%s", a);
    *y = readdata(a);
    return 0;
}

---

Edit: I realise I haven't allocated any space for y, but because it is a pointer shouldn't it just be able to use the space allocated for the array in the function readdata

> Is it possible to pass pointers between functions?
Yes, do whatever you like - declarations and allocations permitting.

Code:

---

#include<stdio.h>

char *getdata()
{
    char *str = "hello";
   
    return str;
}
int main()
{
    char *p;
   
    p = getdata();
   
    printf("%s",p);
   
    getchar();
    return 0;
}

---

The sample code gives you the solution for your problem. I terms of returning the char * pointer to the main.

ssharish2005

getdata should return const char*

And str itself should be const, because string literals are constant.

Thanks, I have it working now. I just have a question about freeing the calloced memory.

Because I need to use this in the main program for furthur operations, how do I go about freeing it. Can I just free the memory by freeing the array that I use in the main program like so:

Code:

---

int main(){
    char a[30];
    char *y;
    scanf("%s", a);
    y = readdata(a);
    printf("%s", y);
    free(y);
    return 0;
}

---

edit: the scanf statement is for the input of the file name to be used (just incase this is unclear).

if readdata returns pointer allocated by malloc/calloc - yes, you can free it in the main function.
But you should check that this pointer is not null before using it.
And better set to NULL after freeing to avoid acidential using of the already freed memory.

In this small sample it is not important, but can be cretical in the big project.

ok, im quite a bit furthur with this project but I have another problem *surprise*.

I have got my program to read the list in now, but I am trying to search it and it seems to start the list at the last word entered and then tries to access the one after it rather than the word entered before it.

I have included the code I have used below although there is quite a lot.

I get a segmentation fault in the searchlist function when trying to access the next item of the list. I think this is a fairly stupid mistake so hopefully something will jump out.

Thanks

Code:

---

char searchlist(list *root, char *word, int a, int b){
   
    if (root->thisnode[0] == '&'){
        return a;
    }
    else if(strcmp(word, root->thisnode) == 0){ 
        a++;
        b++;
        searchlist(root->next, word, a, b);
    }
    else{
        a++;
        searchlist(root->next, word, a, b);
    }
    return 0;
}

list *insertlinkedlist(char *x){
    list *a;
    char y[50];
    int b;
    int c;
    int e;
   
    b = 0;
    e = 0;
   
    while (x[b] != '\0'){
          c = 0;
         
          while (x[b] != ' '){
                y[c] = x[b];
                b++;
                c++;
          }   
          y[c] = '\0';

          a = insertlist(y, a);
          b++;
    }
    y[0] = '\0';
    a = insertlist(y,a);
    return a;
}

list *insertlist(char hd[50], list *a1){
    list *a;
    int b;
    int c;
   
    b = strlen(hd);
    a = calloc(1,sizeof(list));
   
    for (c = 0; c < b; c++){
        a->thisnode[c] = hd[c];
    }
   
    a->next = a1;
    return a;
    free (a);
}

int main(){
    char a[30];
    char b[50];
    char *y;
    list *z;
    int c;
   
    scanf("%s", a);
    y = readdata(a);
    printf("%s", y);
    z = insertlinkedlist(y);
   
    printf("\nEnter word for retrieval:");
    scanf("%s", b);
    c = searchlist(z,b,0,0);
    printf("%d", c);
   
    free(y);
    free(z);
    return 0;
}

---

what I see in your searchlist function

in the main you call it as searchlist(z,b,0,0)

Code:

---

char searchlist(list *root, char *word, int a, int b){
   
    if (root->thisnode[0] == '&'){
        return a;//that is 0
    }
    else
//do some stuff but always got to the bottom line
    return 0;
}

---

so your search always returns 0; Right?

well a is incremented in the program which then calls itself, so it shouldn't be 0 when the search gets to &, and the program would not compile without the return 0

also is it possible to return two values, as I need a and b to be returned to the main program or will I need to insert them both into an array.

the problem line is:
[code]
searchlist(root->next, word, a, b);
[\code]

as root->next seems to be set to an invalid memory address.

thanks for your help

Quote:

---

Originally Posted by manutdfan

well a is incremented in the program which then calls itself,

---

yes, but return values of the subsequent calls are ignored and function goes directly to the return 0; statement

when I debug it, it seg faults when it tries to re-call itself as the root->next address is invalid.

although I have changed the return now so it returns a instead of 0 but I have the same problem.

Quote:

---

Originally Posted by manutdfan

when I debug it, it seg faults when it tries to re-call itself as the root->next address is invalid.

although I have changed the return now so it returns a instead of 0 but I have the same problem.

---

it indicates the problem in your insert function

for example first call to insertlist function is made with uninitialized var a, so you set the next pointer in the first entered node to the ramdom value...

It seems to me that you also have some problems in your 2 loops (what will happen if the inside loop come to the 0 char?)

how would I solve this problem? because the way I have stored it isn't the last thing stored using the insertlist function the head of the list. As all the pieces of data are linked to the one added before it.

As it starts at last one entered shouldn't it seg fault when it reaches the first item inserted in the list?

Insert at the end instead of the beginning. Pretty simple.


Quzah.

I was messing about with the search function to see if there was anything wrong in it, and I found that the root->next is connected together correctly.

I used the following code to test whether hello would actually change to the next word in the list when it passes through the first time and it does. The memory address match up and all, so I can't really understand why it seg faults as I thought this only happens when trying to access a memory location that is unavaliable (which the first one isn't, even if the last one it would test would be).

Code:

---

char searchlist(list *root, char *word, int a, int b){
    list *hello;
    hello = root->next;
    if (root->thisnode[0] == '&'){
        return a;
    }
    else if(strcmp(word, root->thisnode) == 0){ 
        a++;
        b++;
        return searchlist(hello, word, a, b);
    }
    else{
        a++;
        return searchlist(hello, word, a, b);
    }
    return a;
}

---

Code:

---

    list *a;
//some code here
          a = insertlist(y, a);

---

a is not initialized when you call insertlist
with your lack of accuraness in the code - you should initialize all the vars you use, even if you don't think it is needed.

pointers should be initialized to NULL, other vars to some artifitial values.

when you use pointers - you should check that each pointer you dereference is not null

so this would be solved be inserting the calloc statement before the function is called rather than in the function?

Quote:

---

Originally Posted by manutdfan

so this would be solved be inserting the calloc statement before the function is called rather than in the function?

---

So this would be solved by
list* a = NULL;

i've changed that now but I still get the same problem, it has me baffled as the root->next node points to the correct memory address but it seg faults.

before you dereference the pointer - check that it is not null

right i've done that now and it has solved the problem, which gives me another one.

The pointer stored in root->next is the memory address of the next word which I know is correct, although it seems to think the pointer is null. why would this happen?

Edit: it seems it does test the words but then doesn't seem to call the function again, what I want it to do is test whether or not the word entered by the user is in the list and how many times it occurs.

Edit: Edit: it searches through the list now but seems to get a pointer error on the last node I think.

duh of course I get a pointer error as it is the start of the list, anyway it now seems to work although b should be the number of times a word occurs in the list and it doesn't always seem to be.

Also is it possible to return both a and b from the same function?

you can pass them by pointer

thanks, I realised I only needed to transfer them back to print out so I have just incorporated the printf statements into the search function.

Just wondering is it possible to condense the printf commands below anymore:

Code:

---

        printf("\n'%s'", word);
        printf(" occurs ");
        printf("%d", b);
        printf(" times.\nRetrieval from list took");
        printf("%d",a);
        printf(" comparisons. ");

---

printf("\n'%s' occurs %d times.\nRetrieval from list took %d comparisons.", word,b,a);

I want to remove apostrophes from my text, but if I use the following statement it thinks there are too many as they are the initialiser for the query. How would I get round this? I was wondering whether it is possible to use ASCII code.

x[b] == '''

thanks

you can use \" to print quote instead of the '

so i should use

x[b] == '\"'

because it doesn't seem to work.

i mean you can write

Code:

---

printf("\n\"%s\" occurs %d times.\nRetrieval from list took %d comparisons.", word,b,a);

---

if you want to do something else - please explain a little bit more

no sorry I am trying to remove all the apostrophes from my list so when it is searched they don't appear in words.

so I was trying to compare each character in the list with an apostrophe to allow me to find and remove them.

my attempt was x[b] == '''

with the highlighted bit being the condition.

You'd need an escape char with that. . . '\'' where the \ means the next char, if not a special char is litteral.

thanks, thats great it works now