Delete node from linked list in c

Question

I'm trying to make a simple chat service (socket programming) in C. Server is a concurrent and can accept multiple connections. I use thread for server and linked list to save socket id. Everything works fine except delete function which I use for deleting a node from linked list. Whenever a client types DONE, I have to delete its socket id from linked list, but it doesn't work properly. Could somebody help me to figure out what do I have to do in delete function.

here is my structure:

struct ClientList {
    struct ClientList *Next;
    int socket;
    char username[100];
    int count;
    FILE *file;
} ;

here is insert function for adding node

void insert(struct ClientList *newItem,int new_s) {
    pthread_mutex_lock(&mymutex);
    struct ClientList *temp = (struct ClientList *) malloc(sizeof(struct ClientList)) ;
    temp->socket = new_s;
    temp->Next = head;
    head = temp;
    pthread_mutex_unlock(&mymutex);
}//insert function

here is delete function

int del(struct ClientList *temp,struct ClientList *newItem) {
    struct ClientList *cur = head;
    if (temp == head) {
        head = temp->Next;
        free(temp);
        return 0;   
    }//if
    else {
        while (cur) {
            if (cur->Next == temp) {
                cur->Next = temp->Next;
                free(temp);
            }//if
            cur = cur->Next;
        }//while
    }//else
}//del

For first node I don't have problem, but for all others it doesn't work.

i have to add my broadcast function which i use to broadcast any messages from any clinet to all. here is broadcast code:

void broadcast(struct ClientList* temp,char buf[MAX_LINE],struct ClientList * newItem) {

    int len;

    pthread_mutex_lock(&mymutex); 

    for(temp = head; temp != NULL; temp  =temp->Next) {
        if (temp->socket ! =newItem->socket) {
            buf[MAX_LINE-1]= '\0';
            len = strlen(buf) + 1;
            send(temp->socket, buf, len, 0);
        }//if
    }//for

    pthread_mutex_unlock(&mymutex);
}//broadcast

In addition to the 2 answers that have already been made, make sure your delete function takes the mutex. Your insert function does it, your delete function should too. — Celada
– Celada, Commented Mar 4, 2013 at 1:16

Justin Edwards · Accepted Answer · 2013-03-04 01:13:41Z

4

You're doing assignment in your second if, not comparison. It should be:

if(cur->Next == temp)

not

if(cur->Next=temp)

answered Mar 4, 2013 at 1:13

Justin Edwards

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Mats Petersson · Accepted Answer · 2013-03-04 01:15:00Z

3

Most likely because of the trivial mistake of only using one equal sign when wanting two:

if(cur->Next=temp)

should be:

if(cur->Next==temp)

(Also remove the extra argument that isn't needed for "del"!)

Tip: if you are using a good compiler, for example gcc, and you enable all warnings -Wall, then it would give you a warning when you make this mistake.

answered Mar 4, 2013 at 1:15

Mats Petersson

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DoxyLover · Accepted Answer · 2013-03-04 01:57:31Z

0

While you actual question has already been answered, here are a couple of additional comments on your delete function:

Once you find the entry to be deleted, there is no reason to continue searching the list. I'd add a break statement after the second free.
You don't have a return 0 statement at the end of the function. Thus, if the entry to be deleted is not at the head of the list, the return values of the function will be undefined.

Neither of these will cause your program to malfunction (unless you are checking the return value) but these are nice to correct.

answered Mar 4, 2013 at 1:57

DoxyLover

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1 Comment

pejman behravan Over a year ago

my question has not been answered yet

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