strcmp in Linked List insertion crashing program - c

Question

As part of an assignment, I'm supposed to implement a singly linked list in c.
I've done this plenty of times before in a few different languages, but after a few hours of pain I've gotten stuck on a problem using strcmp.
This is the structure I'm using:
typedef struct node {
char *name;
float score;
struct node *next;
} node;
The problem is specific to the insertion function, which is supposed to be similar to an insertion sort, since I need to have the nodes in the list sorted in alphabetical order.(my professor specified that the insertion function does the sorting, despite not calling it an insertion sort).
void insert(node **start, char *name, float score) { // to insert a record into the linked list sorted by name in dictionary order.
//create new node
node *n_node = new_node(name, score);
node *current;
current = *start;
if (current != NULL) { //-----------if list is not empty
node *prev = NULL;
if (current->next != NULL) { //--if list has more than 1 element
while (current != NULL && strcmp(name, current->name) > 0) { //cycle through list to sorted insertion point
// ^^^^^^^Problem Here^^^^^^^^
//while name is greater than current name, means lower on alphabet (z>a)
prev = current;
current = current->next;
}
if (current != NULL) { //-----not at end of list
//once current is not < new node, connect between prev and current
prev->next = n_node;
n_node->next = current;
} else { // ------------------at end of list
prev->next = n_node;
}
} else { //-----------------------list has only one element
current->next = n_node;
}
} else { //--------------------------List is empty - assign new node as first element
*start = n_node;
}
}
The problem is that my program crashes and burns without any errors or warnings (I'm using eclipse with CDT).
The program works fine when
while (current != NULL && strcmp(name, current->name) > 0)
is modified to
while (current != NULL /*&& strcmp(name, current->name) > 0*/).
It seems obvious to me that name or current->name are causing a problem with the operation of strcmp, but I can't seem to get around that.
Edit:
I'll add that this function is called from another function, which retrieves and tokenises strings from a file containing pairs of names and marks, but my testing hasn't suggested that it passes a bad string or characters via the call.
For some extra detail, here's my new_node function:
node *new_node(char *name, float score) {
node *new = (struct node*) malloc(sizeof(struct node));
new->name = malloc(strlen(name) + 1);
strcpy(new->name, name);
new->score = score;
new->next = NULL;
return new;
}
(I realise using new as the name of the node isn't smart, and I will change that)
and the function that calls insert:
int data_import(node **startp, char *infilename) { // to import data from the file and insert .
int max_line = 100;
char line[max_line];
char delimiters[] = ",";
char name[500] = "";
char *namep;
namep = &name[0];
float score = 0.0f;
int i = 0;
FILE *fi;
char *token;
// open file to read
fi = fopen(infilename, "r");
if (fi == NULL) { // Cannot open the file.
perror("error");
return 0;
}
// read each line, increase counter, retrieve data
while (fgets(line, max_line, fi) != NULL) {
//fputs(line, stdout); //console output confirmation
token = strtok(line, delimiters);
strcpy(namep, token);
token = strtok(NULL, delimiters); //increment token to mark variable
score = atof(token);
insert(startp, namep, score);
i++;
}
//close file
fclose(fi);
return i;
}

Answer 1

what happens if you have element called apple as your first element and you try to add element called about ?
you will be thrown out of below while loop straight away and your prev will be unassigned :
while (current != NULL && strcmp(name, current->name) > 0) { //cycle through list to sorted insertion point
// ^^^^^^^Problem Here^^^^^^^^
//while name is greater than current name, means lower on alphabet (z>a)
prev = current;
current = current->next;
}
this particular part looks suspicious to me :
after that you will enter in below routine :
if (current != NULL) { //-----not at end of list
//once current is not < new node, connect between prev and current
prev->next = n_node;
n_node->next = current;
}
as your *prev is unassigned and you try to access it (prev->next = n_node;).you will get crash here.