Making generic function to load items into linked list - c

Question

OK beginning C programmer here. What I'm attempting to do is create a function that populates a linked list from a text file. What I've done so far is to use fgets() and strtok() to iterate through the text file and I'm trying to load the tokenized strings into a function to populate the linked list. First off, when I use strtok, how do I capture the tokenized strings into char arrays or strings? So far, I've tried something like this:
char catID[ID_LEN+1];
char drinkType[1];
char itemName[MAX_NAME_LEN + 1];
while((fgets(line, sizeof(line), menufile)) != NULL) {
token = strtok(line, "|");
strcpy(data,strdup(token));
addCatNode(menu, catID);
printf("%s\n", catID);
i++;
while(token){
if(token)
{
strcpy(drinkType,strdup(token));
addNodeItem(&menu, drinkType);
strcpy(itemName,strdup(token));
addNodeItem(&menu, itemName);
token = strtok(NULL, "|");
}
}
}
but somehow I don't think that's the right approach. And of course when I try and load the data into the addNodeItem() function, whose prototype I've written like this:
void addNodeItem(BCSType* menu, char *nodeitem);
and try and add the item using this notation:
category->nodeitem
the compiler tells me that there is no member named 'nodeitem' in the struct. Of course there isn't, but I'm trying to load the name from the strtok() part, so how do I get the addNodeItem() function to recognize the name that I'm trying to pass into it? Very confused here.
The "category" struct in the linked list looks like this:
typedef struct category
{
char categoryID[ID_LEN + 1];
char categoryName[MAX_NAME_LEN + 1];
char drinkType; /* (H)ot or (C)old. */
char categoryDescription[MAX_DESC_LEN + 1];
CategoryTypePtr nextCategory;
ItemTypePtr headItem;
unsigned numItems;
} CategoryType;

Answer 1

There are several issues here, but for starters, strcpy(drinkType, strdup(token)) doesn't make a lot of sense.
token is a pointer to a portion of your input string, with the '|' separator replaced by a NULL.
strdup allocates strlen(token) worth of memory and copies the contents of token. So far so good. It returns the address of the new memory, which you don't store anywhere, so you can never free() it. This is a leak, and you could eventually run out of memory.
strcpy(drinkType,strdup(token)) copies that new memory into the memory pointed to by drinkType. Thats only 1 character. I don't know if that is big enough. Neither do you, since there could be anything in the file you are loading. This is a bug waiting to happen.
And then it seems like the addNodeItem() function is missing something. You are passing a value that represents one of the possible values in the structure, with no way of specifying which one. You would have better luck creating a local copy of CategoryType, assigning all the information from the tokenizer, and then copying the whole thing into a new node.
outline of algorithm:
while lines:
CategoryType newCat
tokenize line
copy tokens into correct members of newCat, using `strncpy` to ensure no overruns.
add newCat to linked List.
For the last step, you need to duplicate newCat before adding it, because it will be overwritten when you process the next line. You can either pass a copy to AddNodeItem, or have AddNodeItem make the copy. (There are other options, but these are probably most straightforward.)