Deleting a user-entered string node from a linked list - c

Question

I am writing a function that is supposed to remove a node of the user's choice from a linked list of students. The program will take user input through a read_line function for the student's name, last name, and email and then 1)locate the node that has these elements, 2) bypass this node, and 3)release the memory occupied by that node. My function will delete any node other than the head node, and I cannot understand if I have an error in my logic.
Here is my function code:
struct student* remove_from_list(struct student *list){
struct student *p;
struct student *cur;
struct student *delete = malloc(sizeof(struct student));
if(delete == NULL){
printf("\nMalloc failed. \n");
}
if(list==NULL){
printf("\nRoster empty. Nothing to remove.\n");
return list;
}
printf("Enter the last name of the student to be removed: ");
read_line(delete->last, NAME_LEN);
printf("Enter the first name of the student to be removed: ");
read_line(delete->first, NAME_LEN);
printf("Enter the email of the student to be removed: ");
read_line(delete->email, EMAIL_LEN);
//to check if student is in the list
for(p=list; p!=NULL; p=p->next){
if(((strcmp(delete->last, p->last))!=0) || (strcmp(delete->first,p->first)!=0)
|| (strcmp(delete->email, p->email)!=0)){
continue;
}
else{
break;
}
printf("\nThis student does not exist.\n");
return list;
}
//to remove any element other than first
for(cur=list; cur->next!= NULL; cur=cur->next){
if(strcmp(cur->next->last, delete->last)==0 &&
strcmp(cur->next->email,delete->email)==0 &&
strcmp(cur->next->first, delete->first)==0){
delete=cur->next;
cur->next = cur->next->next;
free(delete);
printf("\nStudent has been removed from the list.\n");
return list;
}
}
cur=list; //to remove first element
if(cur->next == NULL){
cur=cur->next;
free(delete);
printf("\nStudent has been removed from the list.\n");
return list;
}
}
My function is not deleting the head node, and I'm not sure if it is a small fix or if there is something fundamentally wrong with my logic. I have seen examples that do this with integer input, but am struggling to implement this in my case. Any help or suggestions are appreciated.

Answer 1

Im not sure if this is what you were intending to do, but it looks wrong logically...
for(p=list; p!=NULL; p=p->next){
if(((strcmp(delete->last, p->last))!=0) || (strcmp(delete->first,p->first)!=0)
|| (strcmp(delete->email, p->email)!=0)){
printf("\nThis student does not exist.\n");
return list;
}
}
But isn't this going to fail unless the first node is the one you want to delete? You're beginning a loop, looking at the first node, and if it doesn't match, you return the list?
Instead of looking for the negative, I think the intention was to loop through the nodes, and if it finds a match, end the loop early - otherwise you want to get to the end of the list to check all of the nodes.
for(p=list; p!=NULL; p=p->next){
if(((strcmp(delete->last, p->last))==0) && (strcmp(delete->first,p->first)==0)
|| (strcmp(delete->email, p->email)==0)){
printf("\nFound a match.\n");
// delete this node and end this for loop early, probably better to use a while loop here, while(strcmp()!=0 etc);
}
}
EDIT
Now that you've got your for loop working to find the record, you might want to do another edit. You find the record with the set of strcmp()!=0 inside the first for loop, which if it finds the record, breaks out of the loop. At this point, you can delete the found record!
That means you don't need to repeat your loop again to delete the record, and you won't have two different blocks of code for if it is the first or subsequent record in the list.
//to check if student is in the list
for(p=list; p!=NULL; p=p->next){
if(((strcmp(delete->last, p->last))!=0) || (strcmp(delete->first,p->first)!=0)
|| (strcmp(delete->email, p->email)!=0)){
continue;
}
else {
// we found a match! Delete it
delete=p;
p->next = p->next->next;
free(delete);
printf("Student has been removed from the list.\n");
return list;
}
printf("\nThis student does not exist.\n");
return list;
}
// should never get here any more
} // end func.
If you really want to keep your code the way it is, because it does work for all but the first record, then you need to get the deleting of the first record to work. The check of == NULL looks wrong, because you only delete the first record if there are no others linked to it? Error in that logic, I feel.
// if we get here, we can assume that the first element matched,
// because otherwise we should never have gotten here
cur=list; //to remove first element
if(cur->next != NULL){ // if there is a next element
// set next to be the first
cur=cur->next;
}
free(delete);
printf("\nStudent has been removed from the list.\n");
return list;
}