Question

So I’m trying to implement a cache in C. I have included a very slimmed down version of my code.

I keep getting this error:

prog.c: In function ‘addtolist’:
prog.c:29: warning: assignment from incompatible pointer type
prog.c:40: warning: assignment from incompatible pointer type
prog.c: In function ‘main’:
prog.c:72: warning: assignment from incompatible pointer type

from this code:

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

struct node_
{
    char * word;
    int filenumber;
    struct node * next;
};
typedef struct node_ * node;

node createnode()
{
    node head;
    head = malloc(sizeof(struct node_));
    head->word = NULL;
    head->next = NULL;
    return head;
}

unsigned int addtolist(node head, char * word, unsigned int limit, int fileno)
{
    unsigned int templimit = limit;
    node temp;
    node temphead = head;
    while(temphead->next != NULL)
    {
            temphead = temphead->next;
    }
    temp = malloc(sizeof(struct node_));
    temp->word =(char*) malloc(strlen(word)+ 1);
    strcpy(temp->word, word);
    temp->next = NULL;
    temp->filenumber = fileno;
    templimit = templimit - (strlen(word) + 1) - sizeof(struct node_)- sizeof(int);
    printf("templimit is size %u\n", templimit);
    if (templimit < limit && templimit > 0)
    {
            temphead->next = temp;
            limit = limit - strlen(word) - 1 - sizeof(struct node_)- sizeof(int);
            return limit;
    }
    else
    {
            free(temp->word);
            free(temp);
            return 0;
    }
}


int main()
{
    node newlist = createnode();
    int i = 0;

    unsigned int limit = 65;
    unsigned int temp = limit;

    while(temp > 0 && temp <= limit)
    {
        temp = addtolist(newlist, "Hello", temp, i);
        i++;
        printf("new limit is - \t%u\nfilenumber is - \t%d\n", temp,i);

    }
    node ptr = newlist;
    while(ptr->next != NULL)
    {
            printf("node %d contains the word %s\n", ptr->filenumber, ptr->word);
            ptr = ptr->next;
    }
    return 1;
}

I honestly can’t figure out what I’m doing wrong… My logic was that, since I was typedef’ing my struct as a pointer, after I created the struct in memory, I would be able to easily step through the ensuing list. Where was the flaw in my logic?

EDIT the initial problem was fixed (I forgot an underscore in my type declaration for struct node_ next;.

Now I’m having another problem: when I try to step through the list at the bottom of my code to print out the words contained in the list, I’m basically not able to step through the list. I keep outputting:

templimit is size 43
new limit is -  43
filenumber is -     1
templimit is size 21
new limit is -  21
filenumber is -     2
templimit is size 4294967295
new limit is -  0
filenumber is -     3
node 0 contains the word (null)
node 0 contains the word Hello

For some reason, it seems that my program isn’t storing my changes to my list in memory after the first iteration. Any ideas on what I’m doing wrong?

Once again, any help would be appreciated, and thanks.

Answer 1

Inside your structure definition you have struct node without the underscore.

you’d better have a forward declaration

typedef struct node node;

and then declare your structure

struct node {
 ...
 node *next;
};

no need to have this underscore stuff and hiding the * in a typedef. That only makes you mix things up easily.