删除链表中的节点

Question

I just started getting into nodes and simple linked lists. While I find linked lists confusing I still start to understand them more and can code them following different tutorials.

But to remove nodes I tried a piece of code that didn't quite work and found another one that did. Except I don't quite get why one works and the other doesn't.

Here is what doesn't work:

void remove_character(Character **head)
{
Character *current=*head,
    *temp=malloc(sizeof(Character));//temporary node to 
     //remove node
char *name=malloc(100);

if(current!=NULL)//if there is at least one node
{
    printf("Enter name: ");
    scanf("%s", name);
}

if(!strcmp(name, (*head)->name))//removes head and 
//makes next node head
{
    temp=(*head);
    (*head)=(*head)->next;
    free(temp->name);
    free(temp);
    current=*head;
}

while(current!=NULL)
{
       if(!strcmp(name, current->name))
    {
        temp=current;//assign node to be removed
        current=current->next;//move to next node
        free(temp->name);
        free(temp);//free removed node
    }
    current=current->next;
}
}

But this works:

void remove_character(Character **head)
{
Character *current=*head, 
  *temp=malloc(sizeof(Character));
char *name=malloc(100);

if(current!=NULL)
{
    printf("Enter name: ");
    scanf("%s", name);
}

if(!strcmp(name, (*head)->name))
{
    temp=(*head);
    (*head)=(*head)->next;
    free(temp->name);
    free(temp);
    current=*head;
}

while(current!=NULL)
{
    if(current->next!=NULL)
    {
        if(!strcmp(name, current->next->name))
        {//if next node is node to be removed
            temp=current->next;
            current->next=current->next->next;
                            //moves to next node
            free(temp->name);
            free(temp);
        }
    }
    current=current->next;
}
}

Basically the second one anticipates one node and links one node further but why should this one work and not the other (which prints segmentation fault right where the removed node was... Nodes seem so easy but are so complicated to manage. Especially when you are bad at imagining how it works.

Answer 1

In your first method you are not proactive.

That is you check for the string after visiting the particular node and once you found the node which is to be deleted you just free it and move further without fixing the list .

Adding one more pointer to point the previous node should fix this issue.

        if(!strcmp(name, (*head)->name))
        {
            /* Code to delete in the head node */ 

            temp=(*head);
            (*head)=(*head)->next;
            free(temp->name);
            free(temp);
            current=*head;
        }
        else 
        {

            /* Code to delete in the rest of the list*/ 
            character *prev=*head;
            while(current!=NULL)
            {
                if(!strcmp(name, current->name))
                {
                    prev->next = current->next;//move to next node
                    free(current->name);
                    free(current);//free removed node
                    break;
                }
                prev = current;
                current=current->next;
            }
        }

In your second method you are proactive.

That is you check for the string before visiting the particular node and once you found out that next node which is to be deleted then you free it and move further after fixing the list .

if(!strcmp(name, current->next->name))   // Found out next node to be deleted
{
     temp=current->next;                 // Get the next node
     current->next=current->next->next;  // Adjust the list by skipping the next node

     free(temp->name);                   // Free the node.
     free(temp);
}