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Help with linked list in C

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Top Forums Programming Help with linked list in C
# 8  
Old 03-31-2011
Linked List Basics

This should be a really detailed explanation of linked lists, code is written in C as well
# 9  
Old 03-31-2011
Quote:
Originally Posted by omega666
if this makes a difference, the way i am doing the list is backwards, so when i want to add something to it, i create a new one in the function, then add the given one (which could be NULL or an actual list) to the next, then return the new one
It's not that. Your very first line of code crashed it -- it never had a chance to crash anywhere else Smilie

Your linked list function should actually work if you just set the first node to NULL. You don't need pointers to pass client_socket_fd though, just a plain int will be fine.
# 10  
Old 03-31-2011
ok i got it to work now
i did
Code:
    client *current;
    current = (client *)malloc(sizeof(client));
    current->next=NULL;
    current = add_client("tttttttt", current, &client_socket_fd);
    current = add_client("ttttttttt", current, &client_socket_fd);
    printf("HERE\n");
    write(1,current->client_name,9);
    printf("\n");
    write(1,current->next->client_name,8);
    printf("\nHERE\n");

Code:
client *add_client(char *username, client *head, int *client_socket_fd) {
    client *current = (client *)malloc(sizeof(client)); 
    current->client_name = username;
    current->client_socket_fd = *client_socket_fd;
    current->next = head;
    return current;
}


and the results are

HERE
ttttttttt
tttttttt
HERE

i dont suppose theres anything still wrong here?

---------- Post updated at 04:23 PM ---------- Previous update was at 04:17 PM ----------

hmm, the above is ok, but when i use it with this function
Code:
int already_there(client *current, char *username) {
    
    while(current) {
        if (strcmp(current->client_name, username)==0) return(1);
        current = current->next;
    }

    return(0);
}

i get a segmentation fault...
# 11  
Old 03-31-2011
Quote:
Originally Posted by omega666
ok i got it to work now
That's wrong. Now there's no way to tell when the list's empty, and have a garbage blank node at the end of your list that might print garbage or crash.

Could you try what I suggested before instead? Sometimes it feels like I'm talking to a wall here Smilie
# 12  
Old 03-31-2011
ok so now i have
Code:
    client *current, *head=NULL;
    current = add_client("tttttttt", current, client_socket_fd);
    current = add_client("ttttttttt", current, client_socket_fd);
    printf("HERE\n");
    write(1,current->client_name,9);
    printf("\n");
    write(1,current->next->client_name,8);
    printf("\nHERE\n");

i dont understand how i am supposed to use head here
Code:
client *add_client(char *username, client *head, int client_socket_fd) {
    client *current = (client *)malloc(sizeof(client)); 
    current->client_name = username;
    current->client_socket_fd = client_socket_fd;
    current->next = head;
    return current;
}

# 13  
Old 03-31-2011
The exact same way you were using it in the first place. Pointers don't do anything mystical. If you pass NULL into your add_client function, you'll get NULL in your add_client function. When you set current->next to it, you're setting it to NULL.

They're just variables. You can copy them around just like you would a float or an int or a structure. The only time pointers do anything special is when you use their contents with the -> operator, the * operator, or the [] operator.
Last edited by Corona688; 03-31-2011 at 05:45 PM..
# 14  
Old 03-31-2011
the use of head was from an example, but i don't understand why its being done, and why my function isn't working the same way (without using head)
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